PIP: Vitamin-B6 interacts with both endogenous and exogenous hormones, and the data presented here concern mostly estrogens (E). E steroids compete with pyridoxal phosphate-dependent apoenzymes for the cofactor in vitro, and a similar effect probably occurs in vivo. Use of E-containing oral contraceptives was associated with an abnormality of tryptophan metabolism similar to that seen in dietary vitamin-B6 deficiency. This was corrected by pyrodoxine administration. However, plasma pyridoxal phosphate concentrations, and other indexes of vitamin-B6 nutritional status, were abnormal in only a minority of these patients. Vitamin-B6 deficiency occurred also in pregnancy,and it was proposed as at least 1 of the factors concerned in the etiology of preeclampsia. Although there was some indication that both corticosteroids and thyroid hormones increase the requirement for vitamin-B6 and modify the activiteis of pyridoxal phosphate-dependent enzymes, these relationships have received limited attention. Current work, however, reveals some interesting associations between vitamin-B6 and the regulation of anterior pituitary hormones. Mediation of these effects seems to occur at the hypothalmic level via the 2 neurotransmitters 5-hydroxytryptamine and dopamine, both of which are synthesized by vitamin-B6-dependent metabolic pathways. Potential clinical application of these results and observations is management of hyperprolactinemia, though controversy over the efficacy of pyridoxine therapy in this situation exists and remains unresolved.