Animal studies and small clinical trials have shown that taurine (2-aminoethanesulphonic acid), a sulphur-containing molecule mainly obtained from the diet in human subjects, has a variety of biological actions that are related to atherosclerosis and cardiovascular functions. However, epidemiological studies of taurine and CHD risk are lacking. We evaluated whether a single measurement of serum taurine could serve as an estimate for long-term serum levels. Serum taurine was measured using HPLC in three annual samples from thirty postmenopausal women selected from the New York University Women's Health Study. Overall, serum taurine values ranged from 62·8 to 245·3 nmol/ml, with a mean of 140 nmol/ml. The intraclass correlation coefficient of a single measurement of serum taurine was 0·48 (95 % CI 0·26, 0·68), which can be improved to 0·65 by using the mean of two annual measurements. The CV was 7 %. These results indicate that the mean of two or more annual measurements of serum taurine is a sufficiently reliable measure of long-term serum levels that can be used in epidemiological studies.