The absorption of 5 mg iron administered in 300 ml water was compared with absorption from 300 ml 0.05 n HCL in 24 subjects with histamine-fast achlorhydria, using a double isotope technique. In ten individuals given ferric chloride the mean absorptions were 2.2% with water and 9.2% in acid; the difference was less marked in the case of the seven subjects to whom ferrous ascorbate was administered (10.9% and 19.3%, respectively). In contrast, acid did not increase the absorption of hemoglobin iron, the mean figures being 13.4% with water and 9.6% with HCL. pernicious anemia; achlorhydria; gastric pH Fe55 and Fe59; radioactive hemoglobin iron Submitted on June 17, 1963