Reduction of hyperprolactinemia by Methysergide (4.4 mg p.o.) and Bromocriptine (2.5 ng p.o.) was studied in 20 patients (7 subjects with pituitary macroadenoma and 13 hyperprolactinemic patients with normal sella turcica). No difference was observed between the effects of the two drugs 4 hours after their administration, with and without respect of the aetiologies of hyperprolactinemia. However the serum prolactin levels were significantly lower 6 hours (n = 11 p = 0,01) and 12 hours (n = 10 p less than 0,01) after Bromocriptine than after methysergide. The difference observed between the two drugs seems to be inherent to their different half-lives.