The safety of hEPO gene therapy was assessed. No env gene of retrovirus was detected in the EPO-transgenic myoblasts and fibroblasts by PCR detection. Malignant transformation of transgenic cells was ruled out by various examinations including cell morphology, chromosome karyotype, soft-agar test, nude mice test and pathology. All the assessments primarily demonstrated that EPO gene therapy mediated by retrovirus was safe.