Four methods were compared as to their suitability for excluding IgA deficiency in the investigation of suspected anti-IgA transfusion reactions. The methods were radial immunodiffusion, passive hemagglutination inhibition, sandwich enzyme-linked immunosorbent assay, and membrane enzyme immunoassay. Parallel testing was performed on sera from 40 patients or blood donors previously found to have anti-IgA and low or undetectable levels of IgA. All test methods identified the 40 sera as having abnormally low IgA levels. The membrane enzyme immunoassay required 10 minutes or less for testing, as compared to 3 hours for passive hemagglutination inhibition, 4 hours for sandwich enzyme-linked immunosorbent assay, and 48 hours for radial immunodiffusion. The membrane enzyme immunoassay offers the potential for a rapid, instrument-free screen of IgA levels and therefore may be useful in identifying those patients with suspected anti-IgA anaphylactic transfusion reactions who are not IgA deficient and do not require IgA-deficient blood components for additional transfusions.