SummaryA 13-year-old Thai female with hemoglobin E-/3-thalassemia was evaluated for anemia and splenomegaly. Globin chain synthesis in a whole cell system revealed an absence of PA chains and excessive a chains. The a/PE + y ratio was 1.26 in bone marrow and 1.90 in peripheral blood. The average y/PE ratio in bone marrow and peripheral blood was 0.36 compared to peripheral blood concentrations of 49% hemoglobin E and 51% hemoglobin F. Homologous red cell 51Cr half-life increased from 22.7 days to 32.8 days after splenectomy. Total circulating hemoglobin increased from 112.9 to 149.7 g. Endogenous carbon monoxide productive (Vco) as a measure of total heme catabolism decreased from 2.00 to 1.54 pmol/hr/kg, Ineffective erythropoiesis was manifested by an increased Vco/Vheme., ratio of 7.52. SpeculationSplenic sequestration may occur as a complicating factor in the anemia of hemoglobin E-P-thalassemia. The mechanism of this disorder is probably related to excessive a chain production and hemoglobin E instability.