One hundred and seventy patients with fluctuating Parkinson's disease participated in an international clinical trial to compare the effects of controlled-released Sinemet 50/200 (mg carbidopa/mg levodopa; Sinemet CR) with standard Sinemet 25/100 (Sinemet STD). The study design involved an 8-week open-label titration (dose-finding) phase (STD and CR preparations given individually during weeks 1-4 and 5-8 respectively) followed by a 24-week double-blind, double-dummy (placebo) treatment period. Drug efficacy was assessed using: (a) data from patients' diaries (i.e. "on-off" periods) (b) the functional disability profile (Northwestern University Disability Scale), (c) the neurological signs and symptoms (New York University Parkinson's Disease Scale, NYUPDS), (d) global evaluations made by the patient and treating physician and (e) the patient's evaluation of sleep. The results indicate that the number of "off" periods and the total NYUPDS score decreased significantly in the patients treated with Sinemet CR compared with those treated with Sinemet STD. Furthermore, the patient's global evaluation was significantly better in the Sinemet CR group. The number of drug-related adverse experiences was similar in the two groups, and only one serious event of this nature was reported.