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1. Total body potassium was measured, by whole-body counting, in children with coeliac disease and in children not having this disease, matched as closely as possible with respect to sex, height, weight and age. 2. The measured total body potassium in children with coeliac disease was not significantly different from that in the matched children. 3. The problems associated with such measurements, particularly those of interpretation, are considered.

1. Exchangeable sodium (NaE), plasma electrolytes and arterial pressure were measured in 121 normal subjects and 91 patients with untreated essential hypertension (diastolic >100 mmHg), 21 of whom had low-renin hypertension. Plasma concentrations of renin, angiotensin II and aldosterone were measured in all hypertensive patients, total body sodium, total body potassium and exchangeable potassium (KE) in some patients. 2. Mean NaE was not different in normal and hypertensive subjects provided the two groups were matched for leanness index. In the subgroup of young hypertensive patients aged 35 years or less mean NaE was below normal. NaE was not related to arterial pressure in normal subjects but in hypertensive patients there were positive and significant correlations of arterial pressure with NaE and with total body sodium. 3. NaE and total body sodium increased with age in hypertensive but not in normal subjects. Partial regression analysis suggested that the correlation of NaE with arterial pressure was not explained by an influence of age. 4. Mean NaE was not increased and mean KE was not decreased in patients with low-renin hypertension. 5. Plasma potassium concentration, KE and total body potassium correlated inversely and significantly with blood pressure in hypertensive patients. These correlations were more marked in young than in old patients. 6. Multiple regression analysis showed that the combination of NaE and plasma potassium concentration ‘explained’ more of the variation of systolic blood pressure in hypertensive patients than it did in normal subjects. Plasma potassium concentration ‘explained’ more of the variation in young hypertensives and NaE ‘explained’ more in older patients. 7. Our findings suggest that changes of plasma and body potassium are important in the earlier stages of essential hypertension and that changes of body sodium become important later.

1. Arterial pressure, plasma electrolytes and exchangeable sodium were measured in 91 patients with essential hypertension and in 121 normal control subjects. Total body sodium, exchangeable potassium and total body potassium were also measured in some of the hypertensive patients. 2. Mean plasma sodium concentration was slightly but significantly lower in the hypertensive patients as a group, but mean values for other electrolyte measurements were close to normal or predicted normal. 3. Exchangeable sodium was not related to arterial pressure in normal subjects but in hypertensive patients exchangeable sodium correlated significantly with systolic and diastolic pressures. These correlations were significant with two methods of expressing exchangeable sodium, in the whole group of patients, in men and in older patients. Exchangeable sodium was not significantly related to arterial pressure in young patients. 4. Total body sodium also correlated significantly with systolic and diastolic pressures in hypertensive patients. 5. Exchangeable sodium was significantly related to age in hypertensive patients but not in normal subjects. Mean exchangeable sodium was significantly lower than normal in young patients. 6. Plasma potassium concentration was not related to arterial pressure in normal subjects but in essential hypertensive patients plasma potassium concentration, exchangeable potassium and total body potassium correlated negatively with systolic and diastolic pressures. These correlations were also significant in young, but not in old patients.

1. A method of measuring changes in the total body content of calcium, phosphorus, nitrogen and sodium in rats by activation analysis in vivo is described. 2. The change in the body content of the elements has been measured in rats on a calcium-deficient diet and in control animals, the body nitrogen being used to represent lean body mass for normalization. 3. There were significant differences in Ca/N and P/N but not in Ca/P ratios between the animals on a deficient diet and control animals at the end of the dietary period.

1. The concentration of potassium in the erythrocytes and the plasma of forty-one normal subjects and twenty-five diabetic patients was measured and the results were used to calculate the total amount of potassium in the erythrocyte mass and the total amount of potassium in the plasma. The total body potassium was measured in a whole-body monitor. 2. In normal subjects a close correlation was found between total erythrocyte potassium and total body potassium and also between total plasma potassium and total body potassium. 3. The regression relation between total body potassium and total erythrocyte potassium in normal subjects was used to predict the total body potassium in diabetic patients. There was reasonable agreement between the measured and predicted total body potassium but there was poor agreement between the measured total body potassium and that predicted from the patient's height and age or height, weight and age.

1. Total body potassium was measured in professional football players before the football season began and at approximately mid-season. The values obtained were significantly higher than in healthy subjects taking only average exercise. There was a significant increase in body potassium as the season progressed. 2. Lean body mass was estimated by four methods and the results were compared. The values of lean body mass, as a percentage of body weight, were significantly higher than in healthy control subjects taking only average exercise and they also increased significantly over the period of the study. 3. The mean erythrocyte potassium concentration was lower pre-season than at mid-season and the pre-season value was also significantly less than in healthy controls. The values before and after vigorous exercise were not significantly different. 4. Conversely, the pre-season mean plasma potassium concentration was significantly higher than in control subjects and than the mid-season value. The mean plasma potassium concentration was higher before vigorous exercise than immediately afterwards. 5. The leucocyte count increased significantly after vigorous exercise, correlating with a decrease in leucocyte ascorbic acid content.

1. Total-body neutron-activation analysis in vivo was carried out in 11 hypertensive subjects to measure simultaneously the total body content of sodium, chlorine, calcium, phosphorus and nitrogen. 2. There was a highly significant correlation between total body sodium measured by activation analysis and total exchangeable sodium measured by a standard isotope-dilution technique (r = 0·92, P < 0·001). Exchangeable sodium averaged 80·3% of total body sodium. 3. The measured values of chlorine, calcium, phosphorus and nitrogen were similar to those for healthy subjects reported by others. 4. Activation analysis in vivo appears promising as an additional tool for investigating sodium metabolism in hypertension, as it is the only method available for determining the total body content of this element. The radiation dose (1 rem) is sufficiently low to permit repeated measurements in the same subject.

1. The oral absorption and the rate of loss from the body of radioactive iron were measured by whole-body monitoring in patients with functioning renal homografts. The incorporation of radioactive iron into erythrocytes was also measured. 2. The results were compared with corresponding values in normal subjects and in non-dialysed and dialysed patients with chronic renal failure. 3. The mean oral absorption and incorporation into erythrocytes of radioactive iron was intermediate between that of normal subjects and of both non-dialysed and dialysed patients with chronic renal failure. 4. The mean rate of loss from the body was not significantly different from that in normal subjects and non-dialysed patients with chronic renal failure but it was significantly less than that in dialysed patients.

1. The fat-free mass (FFM) of ten male and ten female subjects was calculated from measurement of (i) height and weight, (ii) skinfold thickness, (iii) body density, (iv and v) total body potassium by two different methods. All the subjects were apparently healthy and in the medium range of body build and they were mainly young adults. 2. The mean FFM of the ten male subjects was similar as calculated by all methods, although comparisons between pairs of methods sometimes produced discrepancies of up to 2 kg. 3. Agreement was less good for the females but, with the exception of one of the potassium methods, still reasonable. 4. The potassium content of the FFM as mEq K/kg of FFM, was compared with the direct analysis of Forbes, Gallup & Hursh (1961) on four male cadavers. The agreement was close for the men but the K content of the FFM in women was lower than that for men. This difference is discussed.

1. The absorption of radioactive cobalamin was measured by a whole-body counting technique in control subjects and in patients with pernicious anaemia. 2. The absorption of cyanocobalamin by patients with pernicious anaemia was decreased by charcoal but not by bile or saliva. 3. The absorption of cyanocobalamin by control subjects was not affected by food but was significantly increased by pentagastrin. With pentagastrin the absorption of cyanocobalamin was significantly greater than that of hydroxocobalamin. The hog intrinsic factor-mediated absorption of cyanocobalamin by patients with pernicious anaemia was significantly depressed by pentagastrin. 4. The effect of increasing the mass of hog intrinsic factor concentrate on the absorption of cyanocobalamin by patients with pernicious anaemia could be described by a function relating the amount absorbed, the mass of intrinsic factor and two constants. The relationship implies that when the mass of intrinsic factor is small the amount of cyanocobalamin absorbed is directly proportional to the mass of intrinsic factor but that absorption approaches a saturation value with increasing mass of intrinsic factor. In physiological terms the function implies that absorption is proportional to the amount of cyanocobalamin attached to receptor sites but that cyanocobalamin attached to receptor sites may become detached and either reattached or lost to absorption. 5. With oral doses of 25 µg and 50 µg, control subjects absorbed more cyanocobalamin and hydroxocobalamin than patients with pernicious anaemia. At both dose levels control subjects absorbed more cyanocobalamin than hydroxocobalamin but no difference was observed in patients with pernicious anaemia. The intrinsic factor mechanism therefore influences amounts absorbed at such dose levels and appears to be a factor in the differences in absorption of cyanocobalamin and hydroxocobalamin. 6. The use of double-tracer techniques makes it possible for each subject to act as his own control in studies of vitamin B12 absorption. The value of this technique is stressed.

1. By using a whole-body monitoring technique iron metabolism has been investigated in patients suffering from chronic renal failure who required regular dialysis treatment. 2. Oral absorption of inorganic iron was low. 3. The incorporation of radioactive iron into erythrocytes was diminished. 4. The rate of loss of radioactive iron from the body was significantly greater than in normal control and non-dialysed patients with chronic renal failure. 5. Iron exchange between dialysate and patient was studied. Patients with chronic renal failure are known to have a decreased rate of erythropoiesis and to develop abnormalities in iron metabolism (Kaye, 1958; Logue, Lange & Moore, 1958; Boddy, Lawson, Linton & Will, 1970). However, considerable controversy exists about the effect of haemodialysis on iron metabolism in such patients (Shaldon, 1966; Eschbach, Funk, Adamson, Kuhn, Scribner & Finch, 1967; Eschbach, Cook & Finch, 1970). The use of a whole-body monitor permitted measurement in a single study of the oral absorption of a tracer dose of 59Fe, its incorporation into erythrocytes and the subsequent long-term rate of loss of 59Fe from the body. We have previously reported the results of an investigation of iron metabolism by using this method in patients with chronic renal failure (Boddy et al., 1970). We now report the results of a similar investigation of iron metabolism in patients with chronic renal failure undergoing regular haemodialysis therapy.

1. Iron metabolism has been investigated in patients suffering from chronic renal failure, using a whole body monitoring technique. 2. Absorption of labelled inorganic iron was decreased. 3. Radio-iron was lost from the body at a rate comparable to that found in normal subjects. 4. The red cell incorporation of radioactive iron was diminished. 5. The results suggest that anaemia in these patients was due to decreased erythropoiesis and not due to iron deficiency despite the evidence of markedly abnormal iron handling presented.