The broad results of the treatment of patients with idiopathic Parkinson's disease who have received levodopa or its variants are reported. 50 patients, 24 males and 26 females, with a mean age of 66.5 years were treated with levodopa, in daily doses ranging from 0.25g to 6.0g or 'Sinemet' in daily doses of 300mg to 750mg. Periods of treatment ranged from 4 months to 8 years, with a mean of 4.02 years. The relationships of patients' age, onset of Parkinsonian symptoms and interval between initial treatment with levodopa and the current clinical state were studied. Patients were classified according to their clnical response into 3 categories: satisfactory response, progressive deterioration or intolerance of levodopa. The proportion of patients in each category was 66%, 22% and 12% respectively. The clinical results of treatment correlated with those of Webster Disability Testing Scale. Analysis showed that the majority of patients tolerated levodopa and showed an initially satisfactory response. Patients who responded well were considerably younger than those who failed to respond. Patients receiving the drug for a shorter period (less than 3 years) showed a better response. After 3 years' treatment, the response declined. Patients who had had Parkinson's disease for more than 4 years appeared to do less well than those with recently diagnosed disease, but many patients responded well even when treatment was initiated 10 years after the onset of symptoms. Patients discontinued levodopa treatment because of psychoses, nausea, dyskinesia or exacerbation of urinary incontinence. The commonest side effects were nausea (34%), postural hypotension (22%), psychoses (10%) and 'on-off' phenomena in 12% of patients.