AbstractABSTRCTSEffects of Bu-Zhong-Yi-Qi-Tang (Japanese name : Hochu-ekki-to) on the resistance againstListeria monocytogeneswere observed in ICR mice orally administered this medicine daily for 10 days. Survival rates were increased by the pretreatment in mice inoculated i.v. with bacteria 1 day after the last administration and in mice inoculated i.p. 4 days after the last administration. After an i.v. inoculation ofL. monocytogenes, the numbers of bacteria in the spleen and liver increased gradually to kill mice by day 5 in untreated group but the bacterial numbers increased slightly by day 3 and decreased from day 3 to day 8 in Hochu-ekki-to pretreated group. After an i.p. inoculation, the number of bacteria in the peritoneal cavity decreased very rapidly within 6h in Hochu-ekki-to treated group compared to that in untreated group. After the administration, number of polymorphonuclear cells increased in the peripheral blood, peritoneal cavity and spleen. In treated mice, macrophages increased in number in the peritoneal cavity and the spleen but decreased in the peripheral blood. Peritoneal macrophages from treated mice showed an enhanced activity to killL. monocytogenes in vitrowithin 60 min after ingestion of bacteria. Hochu-ekki-to may augment the host defense againstL. monocytogenesthrough the activation of macrophage series during an early phase of infection.