Cabergoline, a new dopaminergic drug with a long-lasting prolactin inhibitory effect, was investigated at different single oral doses administered to puerperas who wished to inhibit their lactation. The study was prospective, randomized and double blind and included 140 puerperas divided into three groups of 40 women each treated with cabergoline and one group of 20 women who received a placebo. The tested doses were 1.0, 0.75 and 0.5 mg, administered orally within 24 hours after delivery. Prolactin levels were measured immediately before drug administration and then after 6 and 12 hours as well as on days 2, 3, 4, 5 and 14 after delivery. At those times the subjects were examined for milk secretion, breast engorgement, pain and possible side effects. In cases of symptoms requiring treatment, an additional 1 mg of cabergoline was administered. Complete inhibition of lactation up to day 14 was obtained in 90.2% of the women given 1 mg, 62.5% of those given 0.75 mg, 45% of those given 0.5 mg and 20% of those given a placebo. Four subjects experienced mild and transient side effects.