The safety and efficacy of Sinemet CR were studied in an open-label, 52-week trial. The study was completed by 156 mildly to moderately ill Parkinson's patients (primarily Hoehn and Yahr stage II to III) at 10 sites. Patients had their treatment optimized on standard Sinemet prior to beginning Sinemet CR treatment. Following titration, there was a median reduction in dosing frequency of 25% (from 4.1 to 3.2 doses/day) relative to the standard Sinemet baseline. Total daily levodopa dosage increased from 623 to 808 mg/day (+33%), a factor consistent with the lower bioavailability of the controlled-release formulation. Mean efficacy scores on the New York University Parkinson's Disease Scale decreased from 7.4 at the end of baseline to 5.8 at 12 weeks, a decline of 20%. The scores remained at this level throughout 52 weeks of treatment. At the end of 1 year of treatment, 60% of patients rated themselves as improved, while physicians rated 64% of the patients as improved. Adverse experiences were similar to those reported by patients taking standard levodopa preparations. Two thirds of the reported adverse experiences occurred within the 1st 3 months of Sinemet CR therapy, indicating that increased length of exposure to Sinemet CR was not associated with an increasing incidence of adverse experiences.