Objective: To test the hypothesis that the nervous system participates in modulating the immune response during experimental African trypanosomiasis caused by Trypanosoma brucei brucei. Methods and Results: Using in situ hybridization and immunochemistry, we studied the effects of splenic sympathectomy on mRNA gene expression and protein production of IL-1β and IL-6 in splenic and peritoneal macrophages (PMΦ) of Sprague-Dawley rats infected with T. brucei brucei and non-infected rats. The enhancements of mRNA gene expression and production of IL-1β and IL-6 by peritoneal macrophages were significantly suppressed by the splenic sympathectomy in both infected and non-infected rats. Conclusions: Our data indicate a probably stimulatory role of the sympathetic nervous system during the host immune response in both normal and T. brucei brucei-infected rats.