In an open pilot study with a parallel group design 30 bottle feeding women were randomly assigned in a two to one ratio to receive either the new dopamine agonist CV 205-502 or bromocriptine for lactation inhibition. Ten women who intended to breast feed served as normal controls. All treated women reached prepregnant prolactin levels within 72 h with once-daily 0.075 mg of CV 205-502 or twice-daily 2.5 mg of bromocriptine, at starting doses of 0.05 mg and 2.5 mg respectively. Fifteen of the 20 women treated with CV 205-502 reported breast symptoms, 50% occurring on days 3 and 4 of treatment. Three of the 10 women treated with bromocriptine had breast symptoms between days 2 and 28. Overall efficacy and tolerance in the two groups was very good. Side effects did not differ between the groups, with the exception of pulse rate in the standing position, which was significantly higher in the bromocriptine treated group than in either the CV 205-502 group (P = 0.02) or the breast feeding group (P less than 0.01). The coagulation tests (fibrinogen, AT III, PTT and APTT) showed no significant differences between the three groups.