Precise and accurate cholesterol measurements are required to identify and treat individuals with high blood cholesterol levels. However, the current state of reliability of blood cholesterol measurements suggests that considerable inaccuracy in cholesterol testing exists. This report describes the Laboratory Standardization Panel findings on the precision and accuracy of plasma or serum total cholesterol measurements in United States clinical laboratories and provides a series of broad recommendations designed to improve performance. The report is divided into 5 sections concerning: (1) why precise and accurate cholesterol measurements are needed; (2) current state of reliability of blood cholesterol measurement: the clinical laboratory, the physicians office and alternate site testing equipment; (3) reliable cholesterol measurements: what is possible; (4) factors contributing to acceptable analytical performance; and (5) resources currently available. A glossary and 28 references are included. (JD)