Sixteen patients, eight with acromegaly and eight with galactorrhea, were treated with pyridoxine (600 mg/day) for a three-month period. The clinical and biochemical changes induced by the drug were compared with those induced by bromocriptine (2.5 to 50 mg/day) administered for the same length of time to the same patients. Pyridoxine induced lowering of growth hormone and prolactin levels in two acromegalic patients. In only one patient with galactorrhea after irradiation of the hypophysis for active acromegaly did pyridoxine treatment stop and galactorrhea and induce renewal of menstrual bleeding without significantly changing the basal prolactin levels. In another patient with a chromophobe adenoma of the hypophysis, it reduced the excessively elevated prolactin levels. On bromocriptine therapy, all the patients reported signifcant clinical improvement paralleled by significant drops in plasma growth hormone and prolactin. It appears that at the dosages administered bromocriptine is preferable to pyridoxine in the treatment of patients with acromegaly or galactorrhea.