We determined the neurotrophic activity of interleukin-2 (IL-2) on primary cultured neocortical neurons from embryonic rat brain. IL-2 clearly enhanced the viability of cultured neurons in a dose-dependent manner. The neurotrophic effect of IL-2 was completely neutralized by IL-2 antibody. Furthermore, expression of IL-2 receptor mRNA was more pronounced in neurons than in other cultured cells such as astroglia and microglia. These results strongly suggest that IL-2 plays certain roles in the central nervous system as a neurotrophic factor.