The effect of Ropinirole on tremor in early Parkinson's disease (PD) was assessed. The results of three multicentre, randomized, double-blind trials comparing ropinirole monotherapy with levodopa, bromocriptine and placebo treatment were analysed retrospectively with respect to improvement of resting tremor and postural/action tremor as measured by items 20 and 21 of the motor section of the Unified Parkinson's Disease Rating Scale (UPDRS). Improvements in resting tremor were significantly better with ropinirole than placebo. There were no significant differences between the effect of ropinirole and those of levodopa (L-dopa) or bromocriptine on resting tremor. Postural/action tremor was mild in these early therapy studies, and there were no significant differences between treatment groups. These results suggest that ropinirole monotherapy is effective in treating resting tremor in early PD. On the other hand, response of postural/action tremor to dopaminergic treatment in early PD was not significantly better than to placebo at the dosages used in these trials.