The effect of combined oral contraceptives containing 158 micrograms of levonorgestrel and 38 micrograms of ethinyl estradiol on vitamin B-1, B-2, B-6, B-12, folates, vitamin A, carotenoids, vitamin E and tryptophan load test was studied in a group of 34 healthy non-lactating women. This was compared to an identical study conducted in another group of 19 subjects who used IUCDs for contraception, and also in two other groups of subjects who were given an additional multivitamin preparation on a daily basis (33 subjects) and on the days when OC was not taken (29 subjects). Assessments were made prior to, and during the third week of the 4th, 7th and the 13th cycles of OC treatment. Urinary xanthurenic acid excretion (XA), plasma vitamin A and the folate content of the sera and red blood cells were significantly increased by OC treatment, although this excessive XA excretion was adequately corrected with 18 mg of daily vitamin B-6 supplementation. The metabolism of the rest of the vitamins was not significantly altered by OC usage. This suggests that a routine use of multivitamin supplement may not be necessary.