Correlations between the plasma concentrations of six distinct carotenoids were determined in 958 participants in a sigmoidoscopy-based case-control study of nutritional factors and colorectal polyps. Plasma carotenoid concentrations were determined by high-performance liquid chromatography following a 12-hour fast. Spearman rank correlation coefficients (r) were used to assess the relationships between carotenoids. We first looked at the group as a whole and then stratified the data by sex, age, smoking status, and ethnicity to determine whether these variables modified the correlations. Among all subjects, concentrations of α-carotene versus β-carotene (r = 0.73) and lutein versus zeaxanthin (r = 0.64) were most highly correlated, likely reflecting common dietary sources among these pairs of carotenoids. In contrast, lycopene was minimally correlated with the other carotenoids (r = 0.23 to 0.27), probably due to this carotenoid having different dietary sources from the others. There was little effect of age, sex, or smoking status on correlations. Correlations between lycopene and the other carotenoids were substantially lower in Asian subjects. While this may reflect distinct dietary patterns in Asians, it could also be due to differences in carotenoid absorption and metabolism. (C) 2000 Elsevier Science Inc.