The serum cholesterol distribution in three geographical areas of Finland was examined during the first and the second FINMONICA surveys in 1982 and 1987. The mean serum cholesterol concentration changed very little during this observation period. In 1987 the population mean (+/- SD) was 6.12 +/- 1.26 mmoll-1 in men aged 25-64 years and 5.96 +/- 1.28 mmoll-1 in women. Only approximately 20% of the Finns had their serum cholesterol at the level which is regarded as desirable by recent international recommendations. The frequency of cholesterol measurements increased in Finland, especially in North Karelia, from 1972 to 1977 but since then no further increase has taken place. From 1982 to 1987 the proportion of subjects whose cholesterol level was over 6.5 mmoll-1 and who reported knowing that their cholesterol was high increased from 27% to 31% in men and from 24% to 34% in women, respectively. It is concluded that approximately 45% of the adult Finnish population is at moderately increased risk and further 33% at considerably increased risk of coronary heart disease because of the elevated serum cholesterol.