Parkinson''s disease (PD) is characterized by a markedly decreased number of nigrostriatal dopaminergic neurons. The pathogenesis of PD is still unknown; among other etiological factors, immunological abnormalities have been suggested. Recently, interleukin-2 (IL-2) has been hypothesized to be an endogenous cytokine that regulates striatal dopaminergic function. We examined the plasma concentrations of IL-1, IL-2, IL-6 and blood levels of ACTH, Cortisol and prolactin of 21 patients with PD without any previous treatment. Age-and sex-matched subjects without any neurological or immune disorders were used as controls. Significantly higher serum concentrations of IL-2 in patients with PD were found. Treatment with antiparkinsonian drugs reduced IL-2 levels in these patients. Our results suggest a functional relationship between central dopaminergic and immune systems and a possible involvement of the latter in the pathogenesis of PD.