This indirect competitive enzyme-linked immunosorbant assay (ELISA) for ferritin, unlike other currently available ELISAS, does not require use of an anti-ferritin antibody-enzyme conjugate. Designed for use on microtiter plates, the method has a precision and sensitivity similar to those of other immunoassays. The detection limit is 20 pg of ferritin per test (corresponding to 2.0 micrograms/L in serum samples). Comparison of results obtained on serum from 57 patients by this method with those from a conventional radioimmunoassay gave a correlation coefficient of 0.92.