Efficiency of cholesterol absorption in the variation of plasma cholesterol level was studied in a random sample of middle-aged Finnish men. Compared with the subjects in the highest decile of plasma cholesterol, those in the lowest decile had a lower cholesterol absorption and, as measured with the serum contents of the cholesterol precursor sterols lanosterol and lathosterol, a higher cholesterol synthesis, the values for the subjects in the middle decile falling in between. Also, the serum content of betasitosterol, a plant sterol used as an additional indicator of cholesterol absorption, was high in the highest decile and low in the lowest decile of the plasma low density lipoprotein (LDL) cholesterol level. Among the whole study group the fractional absorption of cholesterol was positively correlated with the plasma cholesterol level, and a negative correlation was observed between the amount of absorbed dietary cholesterol and the cholesterol synthesis. Thus, the efficiency of cholesterol absorption has an important role in the determination of the plasma cholesterol level among the Finnish male population.