Data from two screening projects on cardiovascular risk factors were used to analyze the trend in serum total cholesterol level in the Netherlands between 1974 and 1986. Cholesterol levels were measured in a single reference laboratory of the World Health Organization throughout the entire study period. Between 1974 and 1980, about 30,000 men and women aged 37 to 43 years (mean age, approximately 40 years) were screened. A decrease in mean serum total cholesterol level was observed until the end of 1977, when it was followed by an increase. This resulted in a net change over the entire study period of -0.07 mmol/liter (3 mg/dl) in men and -0.03 mmol/liter (1 mg/dl) in women. Between 1981 and 1986, about 80,000 men aged 33 to 37 years (mean age, 35 years) were screened. During this period, a decrease of 0.20 mmol/liter (8 mg/dl) in the mean total cholesterol level was observed. In spite of the decline in the mean total cholesterol level, the prevalence of cholesterol values of greater than or equal to 6.5 mmol/liter (greater than or equal to 251 mg/dl) in young adult men was still high in 1986 (16 percent). A further reduction is therefore desirable. The decline in the mean total cholesterol level in young adults might indicate that a further decline in mortality from coronary heart disease can be expected.