The effects of MDMA on antibody stimulation were studied in female rats. Quantity of IgM and IgG antibodies and two immune factors, IL-6 and IFN-g, were measured after rats were simultaneously challenged with MDMA or vehicle and an antigen-stimulating factor. MDMA reduced production of IgG antibodies, specifically reducing IgG2a antibodies, but it had little effect on production of IgM antibodies. MDMA reduced production of IFN-g but not IL-6. These findings suggest that, like other drugs (ethanol, d-amphetamine), MDMA, dampens immune response, specifically to viral infection. These findings are somewhat comparable to those reported in human studies (e.g. Pacifici et al, 2001) indicating that MDMA suppresses Th1 (pro-inflammatory) and enhances Th2 (anti-inflammatory) immunity.