SummaryDuring the initial phase of a prospective cardiovascular epidemiological study, the dosage of the serum cholesterol level was performed in 960 male subjects, most of them having a sedentary life, age varied from 40 to 59, all persons employees of a great Brussels' parastatal organization.The distribution we observe is characterized by a mean level of 240,4 mg/ml with a standard deviation of 43.These values are very similar to those found in U.S.A., in comparable populations. A significant increase of the mean cholesterol level is observed in subjects with ischaemic heart disease. The same is found in subjects suffering from hypertension. There is a low but significant correlation between the cholesterol level and the arterial pressure, especially diastolic, the stature and the corpulence index, particularly the relative weight, the Davenport index and the skinfold thickness.The relation between the cholesterol level and thearcus senilisis very significant. No significant correlation is observed with the weight or the age, although the mean cholesterol level is significantly higher during the sixth than during the fifth decade.Generally, these data are in agreement with those established in other countries having a high standard of life, as far as the studied populations are homogenous and sufficiently numerous. The importance of the associations we found is still more striking, since the serum cholesterol level has a strong variability and since there is no healthy reference population, neither from the clinical, nor from the biological point of view.