Anemia is observed in a considerable number of patients with Chohn\u27s disease (CD). Iron absorption was investigated, using radioactive iron (^FeCl_3), in 12 normal subjects (controls), seven patients with iron deficiency anemia (ID), and 23 patients with CD. After oral administration of 1 μ Ci of ^Fe with 4 mg of FeSO_4 as a carrier, serum ^59Fe levels were determined for approximately three hours with a liquid scintillation counter. The proportion of iron remaining in the body two weeks after administration was also determined as the absorption ratio by whole-body counting. In investigating the factors affecting the absorption ratio, erythrocyte count, hemoglobin, total protein, albumin, serum iron (Fe), serum transferrin (TS), and serum ferritin were used as dependent variables, and were subjected to a multiple regression analysis for the prediction of the absorption ratio. The analysis revealed that hemoglobin and ferritin levels correlated significantly with the absorption ratio. The absorption ratio was not useful in differentiating between ID and CD patient, while both TS and ferritin were useful in differentiating between CD, ID and normal subjects. The time-course change in serum ^Fe after administration of ^Fe showed slightly higher levels in ID and CD than in controls