92 patients with Parkinson's disease not previously treated with levodopa were considered as eligible for this triple-blind trial. Patients were allocated at random to treatment with either levodopa + benserazide ratio 4:1 (Madopar) or levodopa + carbidopa ratio 10:1 (Sinemet) using dosage schedules recommended by the manufacturers which they had to adhere to for 6 months. Unless prohibitive side-effects occurred daily maximum dosage of 800 mg levodopa + 200 mg benserazide respectively 1,500 mg levodopa + 150 mg carbidopa were obtained after 6 weeks and 3 weeks, respectively. The effect of the two schedules on the Parkinsonian symptoms were equal and appeared equally fast. The frequency of gastrointestinal side-effects and involuntary movements were significantly higher and more severe for Sinemet than for Madopar. These side effects are usually symptoms of levodopa overdosing, but whether or not a different dosage schedule with Sinemet would have given fewer side-effects without concurrent lower efficacy remains open to speculation. The treatment schedules did not differ with regard to other side-effects and influence on blood pressure. Neither treatment seemed to influence liver function, renal function and hematological parameters in a statistically way.