PIP: The urinary excretion of quinolinic acid and some other tryptophan metabolites has been determined after a 2-g L-tryptophan load in a deoxypyridoxine-treated subject, in 20 women receiving estrogen-containing oral contraceptives, in and a control group of 12 women taking no steroids. In both situations there were increases in the excretion of quinolinic acid and 3-hydroxyanthanillic acid, as well as 3-hydroxykynurenine and xanthurenic acid. These changes were reversed by pyridoxine administration and are considered to reflect an inhibitory effect of estrogens and deoxypyridoxine on vitamin B6 dependent enzymes. Although the principal enzyme of the tryptophan-nicotinic acid ribonucleotide pathway affected by imparied pyridoxal phosphate function is kynureninase, the present results are consistent with the existence of an unidentified enzyme beyond the formation of 3 hydroxyanthranilic acid requires the coenzyme.