To clarify a role of immunoregulatory T cells in the pathophysiology of autoimmune hemolytic anemia (AIHA), we investigated T cell subsets in the peripheral blood of 15 patients with AIHA by two color analysis using flow cytometry. Consequently both CD4+ cells and CD4+CD45RA+ cells decreased in proportion, irrespective of the disease activity (active or remission phase). CD4+CD45RA+ cells are regarded as naive T cells. Incidentally the ratio of CD45RA+ cells in CD4+ cells also fell in the low level in active phase, but it recovered to the normal ratio in remission. On the other hand, CD8+ cells and CD8+ +S6F1+ cells that may represent activated cytotoxic T lymphocytes increased in active phase and then both entered the normal range in remission. These findings suggest that AIHA could be caused partly by the alternative balance of CD4+CD45RA+ cells probably constituting a member of IRT and moreover by the activation of CTL.