The nationwide multicenter collaborative study for evaluating the monotherapy of Parkinson’s disease with bromocriptine for a period of 5 years from 1986 was reviewed last year. The present report summarizes the follow-up in its 6th year: it includes 30 patients with Parkinson’s disease who continued to receive bromocriptine monotherapy for 6 years and 66 patients who received bromocriptine-levodopa combination therapy during the same period. The mean daily dose of bromocriptine in the 6th year was about the same in the two groups (11.9 and 12.2 mg). In terms of Hoehn-Yahr’s severity grade, severity increased in 20% of the patients undergoing bromocriptine monotherapy, whereas of the patients in the bromocriptine-levodopa combination group it was 45%. Wearing-off phenomenon was not seen in the bromocriptine monotherapy group. By contrast, 30% of the patients in the combination therapy group manifested this phenomenon which, when it occurred, invariably followed the administration of levodopa. Absence of the wearing-off phenomenon implies that bromocriptine has a direct protective action on degenerating substantia