Constipation is a frequent symptom in Parkinson's disease. In this study colonic transit time was measured in 20 patients and 20 sex- and age-matched controls. Colonic transit was normal in all but two of the controls. In 16 patients with Parkinson's disease the average colonic passage was 5 to 7 days. For four patients transit-time was within normal limits. The delayed transport affected all sections of the colon. There was no obvious dependence on age, sex, presentation of the disease, physical activity, or medication. In our opinion, lesions of the autonomic nervous system are responsible.