Several values of immunologic function were studied and correlated with disease activity and extent in 14 patients with alopecia areata, alopecia totalis, or alopecia universalis and in a concurrently studied age- and sex-matched control group. As compared with the control group, the patients showed a significantly increased incidence of autoantibody formation, increased concanavalin A-induced suppression of the normal lymphocyte response to mitogens, an increased proportion of suppressor-cytotoxic cells in the peripheral blood, and a decrease in the absolute B-cell count. Absolute total T-cell counts, quantitative serum immunoglobulin determinations, and lymphocyte proliferation after exposure to the mitogens--concanavalin A, phytohemagglutinin, and pokeweed--and to tetanus antigen were comparable for both groups. Neither the percentage of concanavalin A-induced suppression of the normal lymphocyte response to mitogens nor the helper-suppressor ratio correlated significantly with the extent of hair loss. However, patients, particularly those who demonstrated spontaneous regrowth of hair, had increased concanavalin A-induced suppression in conjunction with an increase in the proportion of peripheral suppressor cells.