The long-term effects of recombinant human erythropoietin (rhEPO) administration in two consecutive cases of paroxysmal nocturnal hemoglobinuria (PNH) with severe anemia are reported. In both patients, a 68-year-old woman and a 66-year-old man, a diagnosis of PNH was made on the basis of severe macrocytic anemia associated with hemoglobinuria, hemosiderinuria and positivity for the sucrose and Ham tests. Subcutaneous treatment with rhEPO, 150 U/Kg body weight daily, was followed in both cases by a progressive increase in hemoglobin concentrations, which thereafter were maintained above 10 g/dL with lower doses of rhEPO and without any relevant side effects for 32 and 29 months of continuous treatment, respectively. A clinical response was observed in spite of elevated baseline serum erythropoietin concentrations, appropriate to the degree of anemia in both patients. These results suggest that rhEPO may be appropriately and safely used in the long-term correction of anemia associated with PNH, and that the response to the pharmacologic doses of rHEPO administered was not dependent on the level of endogenous erythropoietin.