OBJECTIVE: To study the effect of polysaccharide peptide (PSP) on the reconstruction of the hematopoietic function in mice irrad iated by lethal dose. METHODS: The characteristics of proliferation of colony forming unit-granulocyte macrophage (CFU-GM) and colony forming unit-spleen (CFU-S) were measured after continuous injection of PSP in mice for seven days with different doses. RESULTS: Injection of 25 mg/kg PSP in mice could promote and in crease CFU-GM proliferation and cell mitosis, markedly enhance survival ratio, survival time and CFU-S. CONCLUSIONS: PSP has significant regulative effects on the reco nstruction of the hematopoietic and the immunologic functions in mice irradiated by lethal dose.