Patients with various immunodeficiency and autoimmune disorders were examined for the proportions of T cells bearing Fc-IgA, Fc-IgG, and Fc-IgM receptors. These disorders included common variable immunodeficiency, systemic lupus erythematosus, ataxia-telangiectasia, selective IgA deficiency, and the Wiskott-Aldrich syndrome. Abnormal proportions (higher or lower than an interval containing 95% of our normal values) of Fc-IgA receptor-bearing T cells (TA) were found in common variable immunodeficiency, systemic lupus erythematous, ataxia-telangiectasia, and selective IgA deficiency. However, the proportion of T cells bearing Fc receptors did not correlate with their functional activity in in vitro immunoglobulin production assays. © 1983.