Prolactin is a multifunctional hormone that exerts many separate functions and acts as an important connection between the endocrine and immune systems. There are increasing researches implicating the role of prolactin in hematopoiesis. Enhanced erythropoiesis in pregnant women and direct erythropoietic effects in vitro of plasma either from pregnant or lactating mice have been reported. Furthermore, regression of erythroblastic leukemia has been observed in a significant number of rats after hypophysectomy. In this study, the effects of recombinant human prolactin (rhPRL) on hematopoiesis were assessed in irradiated mice. Mice were treated with rhPRL for five consecutive days after exposure to a lethal dose or a sub-dose irradiation. Prolonged survival rate and increased erythropoiesis were observed in the irradiation-induced myelosuppressive mice. It was concluded that rhPRL might act on erythropoiesis and could be a potential candidate for the treatment of irradiation-induced myelosuppresion in clinic. Cellular & Molecular Immunology.