Serum cholesterol level was studied in normal subjects in Kasakake Village. The serum cholesterol levels increased significantly with age, from the third to the fifth decade in males and from the third to the seventh decade in females. Thereafter, the levels were maintained in males while declined in females. The mean peak values (+/- SD) were 178 +/- 31 mg/100 ml in males and 207 +/- 37 mg/100 ml in females. The presumptive values of the zero-year-old obtained from the regression lines calculated from the plot of serum cholesterol values against age were 129 mg/100 ml and 112 mg/100 ml in males and females respectively. Throughout the age-range examined in females, the serum cholesterol level was well correlated with the relative body weight determined with modified Broca's method. A similar, but less obvious correlation was demonstrated in males. However, there was not comparable change in the relative body weight against the trend of the serum cholesterol level in both sexes. In the babies normally delivered with full term, the mean cholesterol level (+/- SD) in the umbilical cord blood serum was 65 +/- 13 mg/100 ml and it increased to 150 +/- 46 mg/100 ml during one to three months after birth which was very close to the presumptive values obtained from the regression lines in the adults. There also was significant correlation between the cholesterol value and the body weight. It is concluded that in normal people, age and relative body weight are major and independent determinants of serum cholesterol level from the start of their life.