Current drugs used for hyperprolactinemia may have severe side effects. Effects and side effects of a new propylergoline derivate (CQP 201-403 SANDOZ) have been evaluated. Twenty-four otherwise healthy women (21-44 years) with hyperprolactinemia (35-318 micrograms/l) without extrasellar extension of pituitary adenomas took part in a randomized, double-blind study. Fasting prolactin levels measured on day 7 was significantly decreased when compared with day 1 (P less than 0.05) in all CQP groups, to 78% with 0.005 mg daily, to 40% with 0.015 mg daily, and to 27% with 0.025 mg CQP per day for one week. The levels in the control group did not change (96%). The area under the curve of the prolactin day curve (1-8 h after drug administration) decreased significantly (P less than 0.05) at all doses when day 7 was compared with day 1, to 77% with 0.005 mg, to 51% with 0.015 mg, and to 37% with 0.025 mg CQP. No change was seen in the control group (96%). Four patients (one on 0.005 mg, one on 0.015 mg, and two on 0.025 mg) experienced orthostatic hypotension while standing blood pressure was to be measured on the first day of treatment, and they had to lie down. CQP 201-403 lowers prolactin levels in hyperprolactinemic women at all doses employed. The effect was seen after the first dose of treatment, and lasted for at least 24 h. The adverse reactions are few and tolerable, and might be less than with current bromocriptine therapy.