The efficacy and safety of bromocriptine mesylate in preventing postpartum breast engorgement and milk secretion were evaluated in 420 normal puerperal women. The usual dose was 2.5 mg twice a day for 14 days. Complete inhibition of the target symptoms was obtained in 97% (409 of 420) of the women after 5 days of therapy. Of 370 women who completed 14 days of therapy, 73.5% (272) were completely symptom free, and the remainder showed only grade I or grade II breast engorgement and secretion. Side effects, primarily nausea, vomiting, and dizziness, were experienced by 3% of the women, and 7% reported rebound engorgement and secretion. It was concluded that bromocriptine is safe and efficacious for the stated indication. Moreover, bromocriptine's apparent lack of thromboembolic complications and low incidence of rebound effects suggest possible advantages over other pharmacologic preparations, ie, estrogen-containing drugs, currently used to prevent postpartum lactation.