A lopecia areata is a tissue-restricted autoimmune disease of the hair follicle, which results in hair loss and baldness. It is often psychologically devastating. The role of T lymphocytes in this disorder was investigated with cell transfer experiments. Scalp explants from patients were transplanted to severe combined immunodeficiency (SCID) mice and injected with autologous T lymphocytes isolated from involved scalp. T lymphocytes which had been cultured with hair follicle homogenate along with antigen-presenting cells were capable of inducing the changes of alopecia areata, including hair loss and perifollicular infiltrates of T cells, along with HLA-DR and ICAM-1 expression of the follicular epithelium. Similar changes were not noted in grafts injected with scalp-derived T cells that had not been cultured with follicular homogenate. These data indicate that alopecia areata is mediated by T cells which recognize a follicular autoantigen.