We studied 10 regular exercising men with Parkinson's disease on levodopa (LD) under two conditions--no exercise and vigorous exercise started 1 hour after LD ingestion. We compared LD levels and motor scores on the Unified Parkinson's Disease Rating Scale (UPDRS). There was a high degree of agreement between plasma LD level and the patients' UPDRS scores 30 minutes later (mean Eta2 = 0.84) in both conditions, with no difference between the two. We conclude that LD levels accurately reflect UPDRS motor function in these patients, and that vigorous exercise started 1 hour after LD ingestion does not influence LD or motor scores.