Forty-four previously untreated patients with early idiopathic Parkinson's disease were treated from the time of diagnosis with submaximum doses of levodopa (mean 420 mg) in combination with a peripheral dopa decarboxylase inhibitor and followed for a minimum period of 3 years. Forty-one gained initial worthwhile improvement, and 17 achieved a reduction in pretreatment disability scores of more than 50%. After 3 years of sustained therapy, only 14 had completely maintained their initial response, and 12 patients were experiencing end-of-dose deterioration; 13 patients had mild peak-dose dyskinesias, but none developed the on-off phenomenon, hypotonic freezing, or end-of-dose dystonia. Retrospective comparison with patients matched for duration of disease and pretreatment severity who had been given maximum tolerated doses of levodopa (a comparable mean dose of 950 mg) showed that the smaller dose regimen reduces peak-dose dyskinesias but not waning of response or end-of-dose deterioration.