A single intraperitoneal injection of the water-soluble cell wall extract from Lactobacillus casei (LCWE) in mice can induce acute inflammatory heart involvement such as cardiac arteritis, similar to the heart lesions in Kawasaki disease. To clarify whether inflammatory cytokines participate in pathogenic mechanisms of LCWE-induced cardioangitis in mice, we studied in vitro cytokine production (IL-1, TNF alpha, and IL-6) from peritoneal macrophages (M phi) stimulated with LCWE in comparison with that of lipopolysaccharide (LPS). LCWE significantly activated M phi of BALB/c in production of IL-1 and TNF alpha compared with LPS. However, the magnitude of IL-6 synthesis by LCWE was approximately similar to that of LPS. These results demonstrate that the pathogenesis of LCWE- induced cardiac lesions may be associated with increased production of inflammatory cytokines.