The effects of Bezoar Bovis on immune responses of ICR Mice were studied. In the present study, the Jerne hemolytic plaque assay (PFC) was used to evaluate the humoral immune response to sheep red blood cells, and macrophage regulatory function was measured by quantitating the production of molecules secreted by macrophages. Bezoar Bovis was given in single daily p.o doses for short term (1, 2 days) or long term (7, 14 days). PFC response for taken 3 days after short term exposure to Bezoar Bovis was increased. The production of nitirc oxide in macrophages was also stimulated. In contrast, long term exposure to Bezoar Bovis resulted in inhibitory effect of Bezoar Bovis on nitirc oxide, $TNF-{alpha}$and IL-6 production in macrophages. These findings suggest that treatment with Bezoar Bovis may result in differential immunological effect depending on treatment schedule.