Six men with prolactin-secreting pituitary macroadenomas and deficiencies of pituitary hormones other than gonadotrophins were treated with bromocriptine for 6 months. During treatment the serum prolactin concentration decreased markedly in all six patients, and in four adenoma size decreased and visual function improved. Two patients who were hypothyroid before bromocriptine treatment were euthyroid during the sixth month of treatment, and the one patient who was hypoadrenal before treatment was euadrenal during treatment. Two of the six men who had subnormal growth hormone secretion before treatment had normal growth hormone secretion during treatment. We conclude that pituitary hormonal functions may improve during bromocriptine treatment for prolactin-secreting pituitary macroadenomas. This improvement may result from decompression of other pituitary cells, because correction of hypothyroidism by bromocriptine was accompanied by conversion from an absent to a normal thyrotrophin response to thyrotrophin-releasing hormone.