We investigated some immunogenic properties of Clostridirtm perfringens enterotoxin (CPE) in vitro using murine J774A macrophages (M Phi) and in vivo using Swiss Webster (SW) mice. CPE was a potent mitogen in vitro, where cell proliferation increased with CPE concentration. CPE was nonmitogenic when Met were concurrently incubated with CPE and interferon gamma (IFN-gamma). M Phi incubated in the presence of CPE induced the synthesis of interleukin-l (IL-1), interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-alpha) and interferon-gamma (IFN-gamma), but not interleukin-2 (IL-2). In vivo, CPE induced a pro-inflammatory cytokine response with striking production of IFN-gamma, IL-1 and IL-6. Regardless of route of CPE entry, serum cytokine levels generally peaked within 1 h of administration and were maintained for 4-8 h. Although CPE engenders an intense immune response during toxicosis, the toxin does not appear to be a superantigen. Death from CPE-induced shock appears to result from various interrelating immunological mechanisms.