The interim results obtained up to the end of the 3rd year of the multicenter nationwide cooperative study on the long-term effects of bromocriptine in parkinsonian patients are reported. Bromocriptine monotherapy could be continued in approximately 33% of the patients at the mean maintenance dose of 11.4 mg/day. The combined use of bromocriptine (11.1 mg/day) in parkinsonian patients already treated with levodopa had a favorable influence on the long-term side effects of levodopa such as the on-off phenomenon and dyskinesia. The beneficial effects of bromocriptine, levodopa and an early combination on parkinsonian symptoms such as rigidity and tremor remained at the end of the 3rd year. However, the effects of each mode of therapy on another parkinsonian symptom, akinesia, ceased by the end of the 3rd year.