We determined the cerebrospinal fluid (CSF) levels of adenosine, a mediator of cerebral blood flow regulation, and neopterin, a macrophage-producing compound, in patients with neurological disorders. Compared to control subjects, the adenosine levels were significantly increased in the patients with acute-stage cerebral infarction (n=12, p<0.0001), acute meningitis (n=10, p<0.0001), or amyotrophic lateral sclerosis (ALS, n=12, p<0.05) (Mann-Whitney U-test). The neopterin levels were significantly increased in the 41 patients with human T-lymphotropic virus type I-associated myelopathy/tropical spastic paraparesis (HAM/TSP, p<0.0001), acute meningitis (p<0.0001), ALS (p<0.05) (Mann-Whitney U-test), or acute-stage cerebral infarction (p<0.005, Student's t-test). In the analysis of 41 HAM/TSP patients, the neopterin levels were significantly correlated with the cell number and glucose levels in the CSF, and were a sensitive marker of inflammation. Several of the HAM/TSP patients with increased adenosine levels were probably complicated with other diseases. The increased neopterin levels in the HAM/TSP group persisted, suggesting that the mononuclear cellular infiltration remained for a long time.