The purpose of this investigation was to evaluate the effects of advancing age on the control of pituitary prolactin secretion. The effects of dopaminergic inhibition and estrogen stimulation of pituitary prolactin secretion were tested both in vivo and in vitro. Estrogen stimulated prolactin secretion in both old and young animals, and elevated estrogen levels in old rats may be partially responsible for elevated prolactin levels. Oral L-DOPA administration induced cycles in old rats but had no effect on prolactin levels in either old or young rats. Injections of L-DOPA lowered prolactin in young but not in old rats, while apomorphine reduced prolactin levels in both groups. The pituitaries of young rats secrete more prolactin in vitro than old pituitaries, further supporting a decrease in hypothalamic DA turnover as a cause for elevated prolactin levels in old rats.