Solid-phase radioimmunoassays have been developed for the detection and quantification of human serum and secretory IgA antibodies to a variety of food, bacterial and viral antigens. Monoclonal antibodies specific for IgA1 and IgA2 and capable of binding to serum and secretory IgA were used. The assays were calibrated by reference to standard serum or purified myeloma proteins bound to solid-phase anti-immunoglobulin reagents, and sigmoid calibration curves were constructed by means of computer programs using 4-parameter logistic or weighted logit-log principles. Polymeric and monomeric forms of IgA antibodies were assayed in fractions separated by high performance size exclusion chromatography. These techniques have demonstrated the expected predominance of IgA1 antibodies in serum, and these included polymeric forms. Saliva contained both IgA1 and IgA2 antibodies, and increased proportions of IgA2 antibodies to lipopolysaccharides and lipoteichoic acid were observed.