Biological effect of bestatin in combination with bleomycin against rat ascites hepatoma AH 66 was investigated. The combined use of bestatin and bleomycin both at a dose of 0.5 mg/kg was found to have a strong inhibition of the tumor growth. The combined effect was also confirmed histologically as follows. In combination group, increase of necrobiosis area in the tumor lesion, augmentation of infiltration of lymphocytes and macrophages around the solid tumors, and marked replacement of necrotic area by fibrous granular lesion were stronger and more rapidly than that in the other group.