The contents of interleukin (IL)-2 and basic fibroblast growth factor (bFGF) were measured in the brain (caudate nucleus, putamen, and cerebral cortex) from control and parkinsonian patients by highly sensitive enzyme-linked immunosorbent assay (ELISA). The concentrations of IL-2 in the brain were in the order of pg/mg protein, and the values were significantly higher in the caudate and putamen from parkinsonian patients than those from control patients. However, the levels of IL-2 in the cerebral cortex showed no significant difference between parkinsonian and control patients. In contrast to IL-2, the bFGF levels in the brain were high and in the order of ng/mg protein, and there was no significant difference in the caudate and putamen between parkinsonian and control patients. Although both IL-2 and bFGF may play important roles in dopaminergic neurons as neurotrophic factors, IL-2 but not bFGF may relate to the compensatory response in the nigrostriatal dopaminergic regions in parkinsonian brain during progress of neurodegeneration.