Blood, pH and bicarbonate were examined in 40 normal subjects and in 53 patients with anemia. Included were 28 patients with thalassemia, 18 with aplastic anemia and seven with iron deficiency anemia. Mean increases in pH of 0–0.04 and decreases in HCO3of 2.3–3.5 mEq/L were observed. Changes were not significantly affected by the degree of erythropoiesis or by the severity of the anemia and were essentially the same in the three groups of patients studied. Typical changes of a mild, uncompensated alkalosis were also produced on four occasions in one transfused thalassemic patient.