Female adult BUF rats (6-8 weeks) received Sham operation (Sham); 70% hepatectomy (PH); Sham or PH with blood transfusion (BT or PH+BT). BUF 7316A hepatoma cells were inoculated subcutaneously in the neck of rats on the operation day. Tumor size was measured from day 7 to 20 after inoculation. Sara and splenic adherent cell harvested on day 5 from Sham and PII rat were added into Mixed Lymphocyte Cultures (MLR), The result showed that tumor growth in Pll or BT rats was significantly promoted as compared to that in Sham rats (P<0.01, P<0.05). The most marked enhancemane of tumor growth was observed in PH+BT rats (P<0.001). Sera and splenic adherent cell from PH rat significantly inhibited MLR (P<0.05). Those results suggest that partial hepatectomy and blood transfusion are responsible for the enhancement of tumor growth. Some immunosuppressive factor might be produced in the process of liver regeneration, and blood transfusion might have an additive immunosuppressive effect.