We report the results of a study on the influence of season and sex on serum concentrations of six carotenoids, retinol, and alpha-tocopherol, as determined by reversed-phase HPLC. The subjects were 111 healthy individuals (54 females, 57 males); 18 additional subjects (10 females, 8 males) were assessed for within-subject longitudinal seasonal variations. Men presented significantly higher retinol concentrations (P = 0.002) and lower concentrations of provitamin A carotenoids--alpha carotene (P = 0.006), beta-carotene (P < 0.001), and beta-cryptoxanthin (P < 0.001)--than women. There were no significant differences between the sexes with respect to nonprovitamin A carotenoids (lutein, zeaxanthin, and lycopene) or alpha-tocopherol. Significant seasonal increments (P < 0.05) in serum concentrations of alpha-carotene and beta-carotene (in summer) and of beta-cryptoxanthin (in winter) were detected in both sexes; in males, lutein was higher in summer whereas in females it rose in spring. No sex-related or seasonal variations were observed in alpha-tocopherol, zeaxanthin, or lycopene. Serum concentrations of provitamin A carotenoids vary according to the individual's sex and season of the year.