Five methods for puerperal lactation inhibition were assessed in a randomized fashion. The 90 women were divided into five groups. Four of these received a pharmacologic treatment: oral stilbestrol (15 mg dd for 5 days), a diuretic compound (bendroflumethazide 15 mg dd for 5 days) by mouth, oral bromocriptine (5 mg dd for 14 days), or an intramuscular injection containing estradiol (10 mg and testosterone (200 mg) esters administered immediately after delivery. To the women in the remaining group only physical methods were applied (breast support and local infra-red waves) and they served as controls. Prolactin plasma concentrations were determined daily for five consecutive days and showed a correlation with the clinical effectiveness of the various treatment schedules. While bromocriptine reduced and stilbestrol augmented prolactin levels, both types of treatment were equally effective in preventing lactation during the observation period. Treatment with a diuretic compound or with an injection of steroids, though less effective than the first two regimens, was nevertheless significantly more efficacious than physical treatment.