Sequence II (Cycled): When hemoglobin levels have stabilized with hydroxyurea once a day and erythropoietin 3 times a week, the hydroxyurea is adjusted so that the amount taken in 7 days is "cycled" over 4 days, and the erythropoietin is cycled over 3 days, with the dose increased twice, every 3 to 4 weeks. Blood pressure and hemoglobin are monitored once or twice a month. Patients with pulmonary hypertension have another echocardiogram and 6-minute walk test once the hemoglobin level is stable.