Recently, it was demonstrated that intracerebroventricular (icv) injection of interleukin-1 (IL-1) stimulated circulating interleukin-6 (IL-6) to a greater degree than intravenous (i.v.) injection of IL-1. The goal of this study was to compare the efficacy of lipopolysaccharide (LPS), injected both icv and i.v., on circulating concentrations of IL-1 and IL-6. Both i.v. and icv injection of LPS stimulated plasma levels of IL-1 to a similar degree. However, i.v. injection of LPS was significantly more efficacious than icv injection of LPS in elevating circulating IL-6. These results demonstrate that like i.v. injection of LPS, icv injection of LPS stimulates plasma levels of IL-1 and IL-6. Increases in circulating cytokines during infectious diseases which are limited to the central nervous system may serve to activate peripheral functions of an acute phase response.