Forty-seven hyperprolactinaemic patients with serum prolactin (PRL) concentrations persistently above 1500 mU/l were treated with the new dopamine agonist CV 205-502 or bromocriptine in a prospective, randomized and double-blind fashion during a 24-week period. Two women had to be excluded because of poor compliance in the first month. Therefore 45 patients remained for evaluation. 81% of the patients in the CV 205-502 group and 70% of the patients in the bromocriptine group normalized their prolactin levels within the study period with a treatment dose as permitted in this protocol. In general serum prolactin normalized within 8 to 12 weeks of treatment. There were no differences between the two tested drugs regarding restoration of the menstrual cycle or disappearance of galactorrhoea. Both drugs gave rise to adverse reactions, especially during the initiation of therapy. However, the adverse reactions reported during CV 205-502 treatment were less severe and persistent than those attributed to bromocriptine. Patient acceptance of the new drug with regard to tolerability was judged by 90% of the women in that treatment group as very good or good, while 75% of those treated with bromocriptine evaluated its tolerability as very good or good. We conclude that CV 205-502 is highly effective in the treatment of hyperprolactinaemia with concomitant restoration of gonadal function and prevention of galactorrhoea. The tolerability of the drug seems better than of bromocriptine and therefore this drug is of value in the treatment of hyperprolactinaemic patients.