Forty-three carbidopa-levodopa (Sinemet)-treated parkinsonian patients with protein-sensitive motor fluctuations were started on the protein redistribution diet within the past 48 months. Thirty patients (70%) are still using the diet successfully after more than 12 months (mean duration, 33.6 months; range, 12 to 48 months). The diet was discontinued in the other 13 cases. In 10 of these 13 patients, the protein redistribution diet was discontinued for a variety of reasons, despite continued sensitivity to dietary protein; in only three patients (7%), those with the most severe and complicated disease, was the protein redistribution diet stopped because of its limited therapeutic benefit. The protein redistribution diet is a simple adjunct to the treatment of Parkinson's disease that can significantly prolong the efficacy of levodopa therapy in many fluctuating "end-stage" patients.