Using the National Cholesterol Education Program's Guidelines for the Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults and the most recent nationally representative serum total cholesterol and lipoprotein data for adults (ages 20 to 74 years) from the second National Health and Nutrition Examination Survey (1976 to 1980), it is estimated that 41% of adults should have lipoprotein analysis after an initial measurement of serum total cholesterol. Furthermore, it is estimated that 88% of those who need lipoprotein analysis, or 36% of all adults aged 20 to 74 years, are candidates for medical advice and intervention for high blood cholesterol levels. We estimate, based on 1986 population data, that approximately 40 million Americans between the ages of 20 and 59 years are candidates for medical advice and intervention. An additional 24 million Americans aged 60 years and older are candidates. Overall, we estimate that about 60 million Americans aged 20 years and older are candidates for medical advice and intervention for high levels of blood cholesterol, although a less intensive approach might be appropriate for elderly patients.