Erythropoietin (EPO) is a glycoprotein synthesized by the kidney, which has a stimulating effect on bone marrow erythroid precursors. It has been identified many years ago, but its clinical use has been developed only since 1985 with the introduction of recombinant molecle (rHuEPO). In the past decade, rHuEPO has been employed in neoplastic as well as in chronic inflammatory diseases associated with anemia, that recognizes a multifactorial pathogenesis: defective endogenous EPO production, impaired erythroid proliferation due to excessive release of inflammatory cytokines, intrinsic abnormalities of erythroid precursors, reticulo-endothelial blockage with reduced erythroid uptake of iron. Anemia of neoplastic diseases, moreover, may be induced or worsened by marrow toxicity of chemotherapy. The efficacy of rHuEPO in these conditions is still unclear.