A sensitive and reproducible enzyme-linked immunosorbent assay (ELISA) has been developed using T cell hybridomas as coating antigen, for detection of Fc receptors for IgA (FcαR). T-T hybridomas were generated from fusions of FcαR+ T cell clones from mouse Peyer's patches with the FcαR- R1.1 T lymphoma cell line. The 2 T-T hybridomas (designated Th HA) used here express FcαR as determined by a rosette method and by ELISA. Th HA cells were cultured under conditions for maximum FcαR expression, were added to individual wells of 96-well EIA plates, and were fixed in situ with glutaraldehyde. Plates were incubated with purified mouse monoclonal IgA, IgM or IgGl and were developed with β-galactosidase-coupled goat IgG antibodies specific for mouse heavy chains. Using the ELISA, both Th HA cell lines were shown to express significant levels of FcαR, lower but detectible FcαR, and no discernible Fcγ1R. Interestingly, the rosette assay only allowed detection of receptors for IgA. When splenic lymphocytes were used, good FcμR and less FcαR expression occurred on these cells as determined by ELISA and rosetting; however, no Fcγ1R cells were detected by either method. Thus, the ELISA is sensitive and reproducible, and allows an objective measurement of FcR expressed on T cells. © 1985.