We examined the role of hepatocyte growth factor (HGF) on the bone marrow suppression by irradiation, by analyzing peripheral blood counts 2 weeks after 7 Gy of total body irradiation in rats. The rats underwent two weeks of continuous intraperitoneal human recombinant HGF injection (50 mg/day) from one day before irradiation using an Alzet osmotic pump. Red blood cell, white blood cell, and platelet counts did not increase with response to administration of HGF. Thus HGF does not show protection against myelosuppression caused by total body irradiation.