Sharply reduced proportions of T cells with Fc receptors for IgG (TG cells) were observed in blood samples from patients with systemic lupus erythematosus (SLE), mainly with active disease. This T-cell subset has previously been shown to be a suppressor in the pokeweed mitogen (PWM)-dependent B-cell differentiation. In contrast, the percentages of T cells with Fc receptors for IgM (TM cells), which have been shown to help immunoglobulin production, were not different from those of normals. TG cells present in the circulation of SLE patients were analysed for their functional capacities in antibody-dependent cell-mediated cytotoxicity and in the suppression of a PWM-induced B-cell differentiation. In both these assays TG cells from SLE patients had normal effector cell activity. This suggests that thr than a qualitative type.