In a study of serum cholesterol and triglyceride concentrations in male physicians, blood was drawn after fasting from 2071 registrants at 17 Canadian medical meetings from 1968 to 1973. Eight regional medical laboratories participated in the study. About two thirds of the samples were analysed in one of two laboratories to diminish method variations. When chylomicronemia, hyperglycemia or extremely high triglyceride values were detected, suggesting nonfasting, the data were discarded. The mean serum cholesterol value for the total study population was 233.9 plus or minus 1.22 mg/dl and the mean serum triglyceride value, 150.5 plus or minus 2.48 mg/dl. The mean values and the prevalence of elevated values (cholesterol larger than or equal to 250 mg/dl; triglyceride larger than or equal to 150 mg/dl) were related to age. Of the total study population 34.7% had elevated cholesterol values and 36.2% had elevated triglyceride values; only the cholesterol value was elevated in 17.5%, only the triglyceride value in 19.6% and both values were elevated in 16.8%. Although this was not a random sampling of Canadian physicians or of Canadian men, our findings of elevated serum lipid values were similar to those in French Canadian civic workers, American executives and Scandinavians, and somewhat higher than those in the Albany, New York and Framingham populations, but distinctly higher than those reported by a recent Nutrition Canada survey.