Total L-erythro-biopterin (T-BP) levels in the ventricular cerebrospinal fluid (CSF) were measured in 43 patients with Parkinson's disease (PD) and 12 age-matched neurological controls. In 5 of the PD patients and 1 control, lumbar CSF T-BP values were also measured. The mean ventricular CSF T-BP level in the PD patients, 15.6 +/- 0.5 pmol/ml (mean +/- SE), was significantly lower than that in the controls (21.3 +/- 1.4 pmol/ml, P less than 0.0001). The mean T-BP concentration in the ventricular CSF was 1.9 times higher than that in the lumbar CSF (P less than 0.0005), indicating a rostrocaudal gradient for the T-BP value in the CSF. When the PD patients were classified according to their predominant clinical features into 24 akineto-rigid (A-R) type and 19 tremor (T) type, there was a significant negative correlation between the T-BP levels and duration of illness only for the A-R type patients (rho = -0.605, P less than 0.005). No such significant correlation was found in the T type patients. These results may indicate a difference of pathophysiological changes in the brain between the 2 types of PD.