We previously reported lower mitogen-induced blastogenic and cytotoxic activity of splenocytes from C3H/OUJ female mice fed 20% soybean oil (SBO) in their diet compared to those fed 5% SBO. The present study examined the kinetics of cell-mediated cytotoxicity using the same animal model and dietary treatments. Kinetic parameters were determined by analyzing the lytic efficiency of splenocytes cultured for various times with several concentrations of radiolabeled P815 mastocytoma cells. The apparent avidity constant (K1/2) of the reaction was not changed by dietary SBO intake (1.0 +/- 0.2 x 10(5) cells for 20% SBO versus 1.3 +/- 0.3 x 10(5) cells for 5% SBO). However, the maximum velocity (Vmax) of the reaction for splenocytes from mice fed 20% SBO was significantly lower than that for splenocytes from mice fed 5% SBO (1.4 +/- 0.2 x 10(4) cells/h for 20% SBO versus 2.3 +/- 0.4 x 10(4) cells/h for 5% SBO, p less than 0.05). The evidence indicates that the rate of target cell lysis, but not the avidity of the lymphocytes for the target cell antigen, was altered by increasing dietary SBO concentration.