A study on the relation between urinary cations and blood pressure was conducted in Wuhan, China. A total of 148 boys aged 7-8 years entered the study from November 23, 1984, to January 13, 1985. Seven consecutive 24-hour urine specimens were collected and blood pressure was measured on the seven successive days corresponding to urine collection. The multiple regression showed that none of the sodium, potassium, calcium, and magnesium cations was statistically significantly related to blood pressure. However, the ratio of sodium/calcium or potassium/calcium in the urine was positively correlated with systolic pressure in multivariate analysis. The results suggest that there may be a complex interaction between sodium and calcium in their effects on blood pressure, and genetic background might have some influences on the sodium/calcium (or potassium/calcium)-blood pressure relation in the 7-8-year-old boys in the study.