Three methods were used to determine the normal ranges for cholesterol and triglyceride in serum of 385 blood donors (289 men, 96 women, aged 18-50 years). Enzymatically determined cholesterol levels had an upper normal range to 6.73-6.99 mmol/l (2.6-2.7 g/l), i.e. lower than with the colorimetric method. The upper range for the triglycerides was 2.28-2.85 mmol/l (2.0-2.5 g/l). Both variables were age and sex-dependent. It is suggested that in assessing lipid levels they should be divided into normal, border-line and definitely abnormal values.