Lumbar cerebrospinal fluid homovanillic acid levels were estimated in 60 patients with Parkinsonism before and during levodopa treatment. There was a slight negative correlation between pretreatment CSF homovanillic acid levels and disability. There was no correlation between pretreatment homovanillic acid levels and clinical response to levodopa. Patients with high pretreatment levels did as well as those with depressed levels. High (normal or near normal) levels of CSF homovanillic acid in a patient with Parkinsonism do not necessarily indicate that the Parkinsonism will not respond to levodopa. These patients should receive the benefit of a trial of levodopa. There was also no correlation between homovanillic acid level during tratment and improvement. Patients with minimal increases in CSF homovanillic acid responded as well as those with greater elevations. Failure of levodopa to increase CSF homovanillic acid significantly does not indicate that the patient will not respond to levodopa and that levodopa should be discontinued. Other factors, such as vitamin B6 consumption, should be investigated.