The rationale for the present study draws its substance from the observation that patients with higher levels of fetal hemoglobin (Hb F) (particularly the Saudi Arabian group), and infants who also have high Hb F levels have fewer crises. Several myelosuppressive drugs, such as 5-azacytidine and hydroxyurea, have been shown to increase Hb F production. The work with 5-azacytidine has had to be abandoned because of the known risk of malignancy.