CV 205-502 (Sandoz), an octahydrobenzol [g]quinoline, is a long-acting dopamine agonist which inhibits prolactin secretion. We conducted a phase 2 clinical study in 10 hyperprolactinaemic women (nine of whom were previously intolerant of bromocriptine) in order to determine (1) the dose at which CV 205-502 exerted its prolactin-lowering effect; (2) the nature of adverse reactions associated with long-term therapy; and (3) whether patients who were intolerant of bromocriptine could tolerate CV 205-502. At first patients were randomized to take initial doses of either 0.02 or 0.05 mg daily at bedtime. Thereafter these doses of medication were gradually increased either to the point of normalizing serum prolactin (to 0.70 IU/l or 20 ng/ml) or to a maximum dose of 0.14 mg daily. The lower initial dose was ineffective and had to be increased in all patients. The higher initial dose (0.05 mg) normalized prolactin in three of five women within 24 h. During chronic administration of the final dose of CV 205-502 (mean 0.09 mg a day), serum prolactin decreased from a mean level of 9.19 +/- 4.9 (SEM) IU/l to a mean level of 1.55 +/- 0.49 IU/l (n = 10 patients). Prolactin was normalized in five patients. Two patients, one of whom had been previously unresponsive to bromocriptine, and another unresponsive to pergolide with regard to prolactin inhibition, were also unresponsive to CV 205-502. Nausea, the side-effect responsible for these patients' previous intolerance of bromocriptine, occurred in six of 10 patients taking CV 205-502 but was much less disabling and did not cause any of the patients to stop this medication. Only one patient taking CV 205-502 discontinued treatment because of adverse effects (light-headedness).