The catechol‐O‐methyltransferase inhibitor tolcapone was compared with the dopamine agonist bromocriptine in an open‐label, randomized trial involving 146 levodopa‐treated parkinsonian patients with end‐of‐dose deterioration of efficacy. Tolcapone was given at a dosage of 200 mg three times daily; bromocriptine was titrated from 1.25 mg once daily at baseline to, at most, 10 mg three times daily by day 24 (mean final dose 22.4 mg/day). After 8 weeks, the tolcapone group had a significant reduction in daily levodopa dose compared with the bromocriptine group (p < 0.05). No significant differences in the “on/off” time and motor disability were seen between the tolcapone and bromocriptine treatment groups. Bromocriptine induced more hallucinations, orthostatic hypotension, and nausea, whereas tolcapone therapy was associated with more muscle cramps and dystonia. These results suggest that when added to levodopa therapy, the two drugs have a different side effect profile, with the advantages for tolcapone being absence of titration and quicker efficacy.