Intervention strategies to combat iron deficiency anemia in developing countries may hasten the development of iron overload in patients with an inherited defect in hemoglobin synthesis. This risk could be diminished if there was a rapid and simple method available for detecting iron overload in population screening programs. We have developed such a method, which is in effect a semiquantitative ferritin measurement based on a modification of a two-site enzyme-linked immunoassay. The assay requires only 2 drops of whole blood and a total incubation time of 90 min. The procedure, which can readily distinguish iron deficiency from even a modest increase in storage iron, has a potentially wide application in settings where a prompt assessment of iron status is required.