Twenty-two hyperprolactinaemic women were randomly allocated to two groups and treated with bromocriptine or the new, non-ergot, long-acting dopamine agonist, CV 205-502. The study was double-blind for 6 months. Four patients in the bromocriptine group, but none in the CV 205-502 group, discontinued the study because of adverse reactions. Adverse reactions in those receiving the new drug were milder and more transient than with bromocriptine. With once-daily doses of 0.075 mg CV 205-502, eight of 11 women achieved normal PRL concentrations after 8 weeks treatment (median (95% confidence limits), 352 (70-987) mU/l) compared with two of nine receiving a divided daily dose of 5 mg bromocriptine (1802 (1205-4438) mU/l) (P less than 0.002). With doses of 0.075-0.15 mg of CV 205-502, 10 of 11 women achieved normal PRL concentrations at 24 weeks compared with three of the remaining seven women on doses of 5-10 mg of bromocriptine. Regular menstrual bleeding was restored and galactorrhoea relieved in the majority of patients, with marginally greater efficacy with CV 205-502. CV 205-502 is highly effective for the long-term treatment of hyperprolactinaemia. It is better tolerated than bromocriptine, is effective in a once-daily dose, appears to be safe, and provides a valuable alternative to the dopamine agonist drugs in use today.