Bromocriptine (CB-154) and the 8-alpha-ergoline CU 32-085, two dopamine receptor agonists, were administered at different times to two series of 22 patients with Parkinson's disease, most of whom took levodopa (plus benserazide) at optimum dosage. The addition of bromocriptine (mean daily dose 32 mg; after 6 months 40 mg) led to a 38.5% reduction of levodopa, while CU 32-085 (mean daily dose 15.2 mg; after 6 months 17.5 mg) permitted a 33.7% reduction in levodopa. The mean dose in two patients on CU 32-085 monotherapy was 55 mg/day. A total of 15 patients tolerated adequate doses of bromocriptine (5-75 mg/day, mean duration of treatment 7.5 months) and 15 patients long-term treatment up to 14 months with CU 32-085 (dose range 1-60 mg/day; mean duration 8.8 months). Both groups showed a significant improvement of "total disability score' at 6 months by 56% and 67%, respectively, and after 6 months by 69% and 69.4%, respectively, with a significant decrease of all types of disability. All patients with fluctuations and "on-off' effects rapidly improved on both compounds. Bromocriptine and CU 32-085 were discontinued in seven patients each (32%) because of adverse effect including mental changes (for with bromocriptine, two with CU 32-085), nausea and vomiting (one and two, respectively), hypotension (one each) and increased tremor plus vomiting (one with CU 32-085). Although adverse effects were similar to those observed with levodopa, CU 32-085 in general showed less severe dyskinesia and mental changes but more frequent nausea than bromocriptine and levodopa. While the results of treatment with bromocriptine and CU 32-085 were comparable, the antitremor effect of the latter drug developed more rapidly, even at low dosage. Both compounds were useful in the management of patients with advanced Parkinson's disease, CU 32-085 having a stronger effect on tremor, bradykinesia, fluctuations and "on-off' effects than bromocriptine.