We have previously demonstrated that extracts of striatal tissue from patients with Parkinson's disease (PD) increase the survival of dopamine neurons in mesencephalic cultures relative to striatal extracts from control patients. In the present study, ventricular cerebrospinal fluid (vCSF) from patients with PD, Alzheimer's disease (AD), and age-matched controls was similarly assessed. vCSF samples were separated into > 10-kDa and < 10-kDa fractions. Cultures incubated with the > 10-kDa fractions from PD and AD patients contained 73 and 13%, respectively, more tyrosine hydroxylase immunoreactive neurons than cultures incubated with vCSF from age-matched controls. This trophic activity was positively correlated with the trophic activity present in striatal extracts from the same patients. The < 10-kDa vCSF fractions from all patient groups inhibited culture growth. These data suggest that the trophic environment in the striatum is altered in PD and can be successfully monitored in CSF.