The relationship between body composition, as measured by body mass index and bioelectrical impedance analysis, and baseline plasma carotenoid concentrations was determined in 36 healthy younger (20-40 y) and older (60-80 y) men and women (nine per group). Changes in plasma carotenoid concentrations after 15 d of consuming a controlled high-carotenoid diet were also correlated with body composition (p<0.05). Older women, who had highest percentage of body fat (38%) among the four groups, showed significant and inverse correlations between body composition (defined by body mass index, percentage of body fat, fat mass and fat free mass) and baseline plasma carotenoid concentrations. Younger women, who had 29% percent body fat, showed a significant and inverse correlation only between body mass index and plasma beta-carotene. However, younger and older men, who had lower percentages of body fat (23% and 22%, respectively), did not show any correlation between body composition measures and baseline plasma carotenoid concentrations. The increases of plasma concentrations of alpha-carotene and beta-carotene after 15 d of consuming a high-carotenoid diet were significantly and inversely associated with percentage of body fat and fat mass in older women only. Thus, fat mass appears to influence serum carotenoid concentrations in only certain subjects (i.e. older women) who have relatively high percentage of body fat.