In this 12-week, randomized, open-label, blindedrater, parallel-group trial, the efficacy, safety, and tolerability of tolcapone and pergolide were compared in parkinsonian patients with a fluctuating response to levodopa. Patients received tolcapone 100 mg three times daily (t.i.d.), with a possible increase to 200 mg t.i.d., or pergolide titrated to a maximum dose of 5 mg/day by week 9 (mean final dose 2.2 mg/day). The trial involved 203 patients. Efficacy variables that decreased from baseline to week 12 with tolcapone and pergolide included "off" time (reduced by 2-3 hours/day), daily levodopa intake, sickness impact profile scores, Parkinson's disease questionnaire (PDQ)-39 scores, and Unified Parkinson's Disease Rating Scale (UPDRS) scores. Improvements in efficacy variables were similar with tolcapone and pergolide, with the exception of improvements in quality of life, which were significantly greater with tolcapone; the relative changes in PDQ-39 score at week 12 were -8.7 and -14.2 (P < 0.05) with pergolide and tolcapone, respectively. Improvements in the investigator's global assessment (IGA) of overall efficacy were recorded in 86% of tolcapone-treated patients and in 78% of pergolide-treated patients. The proportion of patients who withdrew because of adverse events was higher in the pergolide group (15%) than in the tolcapone group (5%). Confusion, hypotension, nausea, constipation, abdominal pain, and dyspepsia occurred more frequently with pergolide, whereas diarrhea and urine discoloration occurred more frequently with tolcapone. Tolcapone was better tolerated than pergolide (P < 0.01) according to the IGA of overall tolerability. We conclude that, in this 3-month study, both tolcapone and pergolide provided improvements in motor fluctuations and allowed reductions in levodopa intake when added to levodopa therapy; intent to treat analysis and a less than maximal dose of pergolide may have biased the results in favor of tolcapone. Tolcapone provided greater improvements in quality of life, was better tolerated, and had a more favorable adverse-event profil than pergolide. © 2001 Movement Disorder Society.