The immunosuppressive effects of safrole were studied in female BALB/c mouse. Mice were given 100,200and 400mg safrole/kg daily for 14days and evaluated on day 15. The day 4 immunogloblin-M antibody response to T-dependent antigen, sheep red blood cells (SRBC) was inhibited dose-dependently in all doses studied. In vitro antibody response to polyclonal antigen, lipopolysaccharide (LPS) by spleen cell suspensions from safrole-treated mice were also significantly inhibited. When safrole was treated for 14days to mice, and mitogen-induced proliferation of splenocytes were assayed on day 15, there were significant suppression of responses to B-cell mitogen, LPS and T-cell mitogen concanavalin A(Con A) at a dose of 400mg safrole/kg. Direct addition of safrole on the splenocyte culture also produced a dose dependent suppression on in vitro antibody response to LPS, and mitogen-induced lymphoproliferatin at doses of 100,200,400 and 800${mu}M$ safrole. The role of metabolic activation in safrole-induced suppression of in vitro antibody response was studied using splenocyte-hepatocyte coculture system. The suppression of in vitro antibody respose to LPS by safrole was not altered when safrole were incubated in the splenocyte-hepatocyte system for 4hr as compared with direct addition of safrole in splenocytes culture. Neither the addition of salicylamide, sulfotransferase inhibitor, nor the addation of inorganic sulfate, sulfation cofactor to the splenocyte-hepatocyte coculture, altered the suppression of antibody response by safrole. These results suggest that the immunosuppression by safrole may not by produced by the reactive metabolites which are mediated in carcinogenesis of safrole.