Nineteen patients with mild-to-moderate Parkinson's disease completed a 1-year open label study of a controlled release preparation of carbidopa/L-DOPA (Sinemet CR). Twelve patients were thought to have improved compared with baseline, and only one was worse. The total daily dose of L-DOPA was not significantly changed, but dosing frequency was almost halved. Patients with complex drug schedules on standard Sinemet liked the drug most. "Wearing off" patients also benefitted from the change, whereas "on/off" patients did not do significantly better on Sinemet CR.