From 1960 to 1980, serum cholesterol levels were determined for three different national surveys of the US noninstitutionalized population aged 20 to 74 years conducted by the National Center for Health Statistics, Hyattsville, Md. Serum cholesterol determinations for each of the three surveys were standardized to the Abell-Kendall laboratory method. Age-adjusted mean serum cholesterol levels decreased by 6 to 8 mg/dL (0.16 to 0.21 mmol/L), or 3% to 4%, between the 1960 to 1962 and the 1976 to 1980 surveys. For men, this represented a decrease from 217 mg/dL (5.61 mmol/L) to 211 mg/dL (5.46 mmol/L) and for women, a decrease from 223 mg/dL (5.77 mmol/L) to 215 mg/dL (5.56 mmol/L). Both declines were statistically significant. Mean serum cholesterol level decreased significantly in whites but not in blacks, and in all education subgroups for whites except men with less than nine years of education. In addition, the percentage of men and women with high-risk and moderate-risk cholesterol levels decreased during this period.