We evaluated the efficacy of cabergoline, a new ergoline derivative, in blocking puerperal lactation in a group of women delivered by cesarean section. In a single-blind controlled trial 36 women were randomly allocated to treatment with cabergoline 1 mg in a single dose p.o. (n = 18) or bromocriptine 5 mg/day p.o. for 14 days (n = 18). Treatment was started about 50 h after delivery. Clinical assessment of breast signs and determination of serum prolactin were performed just before treatment and at 3, 5, 7 and 14 days. In the cabergoline-treated group milk secretion was inhibited in 17 women (94.4%). Maximum decrease of serum prolactin was -89.7% at 5 days, and the prolactin-lowering effect of cabergoline was still present at 14 days. In the bromocriptine group milk secretion was inhibited in 16 women (88.9%). Maximum prolactin decrease (-86.9%) was reached at 3 days. Persistent side effects were comparable in the two groups. This study demonstrates that a single oral dose of 1 mg cabergoline is as effective in suppressing puerperal lactation as a full treatment with bromocriptine, even in women delivered by cesarean section.