The efficacy of controlled-release Sinemet was evaluated in a 52-week open trial involving 20 patients (14 men, 6 women; mean age 66 years, range 56 to 82) with idiopathic Parkinson's disease of 8 years' mean duration. The mean daily dosage of levodopa was 662.5 mg (200 to 1600 mg) on entering the study and 800 mg (200 to 2400 mg) after 52 weeks. The mean number of daily doses was reduced from 5.0 (2 to 16) at entry to 3.3 (1 to 6) after 52 weeks. Rigidity, tremor, and bradykinesia were scored at 3 intervals during baseline and 8 intervals during the study on controlled-release levodopa. All parameters improved, with maximum improvement seen at week 12. Side effects were less frequent on the controlled-release preparation. After 5 months, 1 patient developed protracted dyskinesia with freezing episodes and end-of-dose deterioration on dose frequency reduction.