To examine whether neutrophils are involved in the pathogenesis of experimental liver dysfunction, we observed the effect of selective in vivo neutrophil depletion by a monoclonal antibody (RP-3) on the pathogenesis of acute experimental hepatic necrosis in rats induced by a preparative injection of heat-killed Corynebacterium parvum and a challenging dose of lipopolysaccharide (LPS) (positive control group). The serum transaminase titer 8 h after LPS injection was reduced by selective depletion of peripheral blood neutrophils as a result of RP-3 treatment (RP-3 group). A kinetic study showed that the serum transaminase titer of the RP-3 group was significantly lower than that of the positive control group from 4 to 24 h after LPS injection. The transaminase level was significantly lower in the group with less than 400/mm3 peripheral blood neutrophils than in the group with a greater number. The effect of RP-3 on the transaminase level was due neither to the injection of cancer ascites nor to RP-3 injection with the accompanying decrease in complement titer. These results suggest that neutrophils play an important role in the induction of liver dysfunction in this system.