OBJECTIVE To determine serum immunoreactive erythropoietin (Epo) and soluble transferrin receptors (sTfR) levels in patients with hemoglobin H (HbH) disease and the correlation with HbH levels and alpha-globin genotype. METHODS Twenty patients with HbH disease were studied. Methods applied included cation-exchange high pressure liquid chromatography for HbH levels, chemoluminescence for Epo concentration, immunoassay for sTfR concentration, and DNA analysis for alpha-globin genotype characterization. RESULTS Serum Epo and sTfR levels were significantly elevated (46.6+/-26.8 IU/l and 5.6+/-1.8 mg/l, respectively) in patients with HbH disease compared to controls (9.2+/-3.3 IU/l and 1.8+/-0.7 mg/l, respectively). Epo and sTfR levels correlated positively with HbH concentration (r = 0.93 and 0.80, respectively). The highest Epo and sTfR values were observed in three patients with the highest HbH levels who all had nondeletion alpha-thalassemia mutations. CONCLUSIONS Epo and sTfR levels are increased in patients with HbH disease; this increase is directly related to the HbH concentration that usually reflects the degree of globin polypeptide imbalance. The correlation of Epo, sTfR, and reticulocyte production index in these patients indicates that anemia in HbH disease mainly is caused by ineffective erythropoiesis and a mild degree of peripheral hemolysis.