Elevation of serum prolaction in response to pipothiazine was of a greater magnitude than that following administration of fluphenazine decanoate. Females weremore sensitive to the neuroleptic-induced disinhibition of prolactin release than their male counterparts. In contrast to reports on short-acting neuroleptics, a ceiling effect on prolactin elevation was not observed when therapeutically effective dosages of long-acting preparations were used. A overall curvilinear relationship between symptoms and prolactin change was observed. The predicted negative relationship between clinical response and prolactin was clearly evident mainly in females on pipothiazine palmitate.