The effects of the water-insoluble fraction of mouse seminal vesicle fluid (WIF-SVF) on lymphocytes was investigated to clarify its role in reproductive immunity. WIF-SVF inhibited the blastogenic response of T-cells to concanavalin-A (Con-A), but it did not inhibit the blastogenic response of B-cells to lipopolysaccharide (LPS). Pretreatment of splenocytes with WIF-SVF did not suppress the blastogenic response of splenocytes to Con-A when treated cells were washed prior to culture. WIF-SVF did not inhibit the proliferation of Con-A activated splenocytes, the response of listeria-immune splenocytes to listerial antigen, or the proliferation of IL 2-dependent HT-2 cells, or the growth of tumour cells (Yac 1 cells, Ehrlich ascites carcinoma cells, EL-4 cells). A listerial antigen-specific immune response was not induced after mice were immunized with both listerial antigen and WIF-SVF. WIF-SVF is mainly composed of protein and its suppressive activity was enhanced by heating at 100 degrees C. These results suggest that WIF-SVF inhibits the responsiveness of T-cells to antigens or mitogens non-specifically at the initial stage.