Retrospective study of 129 patients treated with dopamine substitution showed that the occurrence of response variations is related to the duration of therapy and not to the nature of the predominant symptom (tremor or hypokinesia and rigidity) or the age of onset of the disease. A relationship was found between the occurrence of response variations and the severity of the disease when levodopa therapy was started. Patients fared worst who were in Hoehn and Yahr stages I and II when levodopa therapy was begun.