To investigate the contribution of nigral degeneration to the development of parkinsonism in the early stages of corticobasal degeneration (CBD), we measured the cerebrospinal fluid (CSF) levels of homovanillic acid (HVA) in patients with early CBD (n = 5), and compared the levels with those in patients with early Parkinson's disease (n = 11) and in normal subjects (n = 13). The mean CSF HVA level in the early CBD group (33.1 +/- 6.0 ng/ml) did not differ significantly from that in the control group (37.1 +/- 12.7 ng/ml), whereas that in the early Parkinson's disease group (19.0 +/- 7.6 ng/ml) was reduced significantly (P < 0.001). This result suggests that neuronal cell loss in the substantia nigra and presynaptic nigrostriatal dopaminergic neuron dysfunction are mild in the early stages of CBD.