ABSTRACT: Seminal plasma displays a suppressive function on many immunological responses. In light of recent findings on the antibacterial activity mediated by different lymphocyte subsets, we have assessed the effect of male inhibitory material (MIM) in this system. Results provide evidence that MIM pretreatment of peripheral blood lymphocytes (PBL) leads to a significant inhibition of antibacterial activity against Salmonella typhi and S. minnesota R345 (Rb). Both CD4+ and CD8+ cell-mediated activities are reduced by this treatment, while another defense mechanism (bacterial binding to PBL) is unaffected. Taken together, these results indicate a role for MIM in the depression of immune response and suggest that lymphocytes mediating antibacterial activity and bacterial cytoadherence are different entities.