Although bromocriptine is the mainstay of treatment of macroprolactinomas, its therapeutic usefulness may be limited by poor tolerance, lack of consistent reduction in serum prolactin levels and tumour size, and the necessity for multiple dosing. Consequently new dopamine agonists have been developed, including the long acting non-ergot agonist CV205-502 which has been shown to date to be consistently effective in reducing serum PRL levels and causing tumour shrinkage. Twelve patients were treated for periods of up to 24 months with CV205-502 in doses ranging from 0.075 mg to 1.65 mg once daily. Clinical and psychiatric assessments, biochemical parameters, tumour size determination, and anterior pituitary function tests were performed regularly. Tumour shrinkage was noted in all patients, and varied from 11 per cent reduction to complete disappearance of tumour. Prolactin levels became normal in seven patients and were reduced by more than 90 per cent in the remaining five. Normal menstruation resumed in six of the eight women, one of whom conceived after one year of therapy; libido returned in all patients. Psychiatric complications occurred in three patients necessitating withdrawal of therapy in one. Significant weight loss was noted in 11 of 12 patients. Triglyceride concentrations fell from 1.5 +/- 0.1 to 1.0 +/- 0.1 mmol/l at 12 months (p = 0.006), and cholesterol fell from 6.3 +/- 0.4 to 5.3 +/- 0.3 mmol/l (p = 0.04). The mean TSH response 20 min following TRH injection fell from 14.3 +/- 2.9 to 8.7 +/- 1.3 mU/l at 2 months (p = 0.027). There was a significant increase in the peak growth hormone response to the insulin stress test from basal median (25th-75th centiles) values of 15 (4.4-25.5) mU/l to 24.5 (9-37) mU/l at 2 months (p less than 0.01) and 31 (19.3-63.5) at 12 months (p less than 0.005). CV205-502 is highly effective in the medical management of patients with macroprolactinomas, reducing prolactin levels and tumour size and restoring normal anterior pituitary function. It is, however, associated with the important side effects of weight loss and psychiatric complications which should be drawn to the attention of clinicians.