Twenty-five consecutive patients with Parkinson's disease, who had been on levodopa for 10 or more years, were studied. Over the 12.9 years of treatment, the average Northwestern Disability Score had increased from 9.6 to 18.9. By this measure, 24 of 25 patients were worse, and one was unchanged. The progression of disability did not involve all pretreatment parkinsonian features equally in any of the patients studied. Instead a distinctive pattern of deterioration was seen: postural reflexes worsened in 24/25, speech in 24/25, and gait in 22/25. In contrast, rigidity was improved or unchanged in 17/25, tremor was improved or unchanged in 17/17, while handwriting was improved or unchanged in 21/22. Finger dexterity which was improved in 5/25, unchanged in 15/25, and worse in 5/25 which seemed to be between these two extremes. These observations demonstrate that some signs of parkinsonism can remain quite responsive to levodopa for more than 10 years while at the same time other manifestations of the disease are no longer as responsive to this form of treatment.