An 8-year nationwide study of bromocriptine monotherapy and combination therapy with bromocriptine and levodopa in Parkinson's disease is reported. Fifteen patients were on bromocriptine monotherapy, and 44 patients on bromocriptine combined with levodopa for a certain time during an 8-year period. By judging from Hoehn and Yahr's grading, 4 of the 15 patients in the monotherapy group were in a better condition than before treatment, while 7 cases remained in the same grading, and only 4 showed deterioration. On the other hand, 26 of 44 patients on combination therapy showed more advanced grading at the end of 8 years compared to the stage at the onset of the trial. Maintenance doses of bromocriptine in the two groups were 12-13 mg per day, and levodopa doses were kept at a relatively low level (310-370 mg per day) during this study period. Whether dopamine receptor agonists have neuroprotective effect or not is extremely difficult to prove in human subjects, but this type of long-term follow-up study might give some clues as to these important questions.