Peripheral blood lymphocytes and the "in vitro' changes of the T-cell count after levamisole treatment were studied in twenty-two patients with systemic lupus erythematosus and in eighteen normal controls using E-rosette assay to quantify T-cells and EAC-assay to quantify B-lymphocytes. T-cell count was significantly lower in the patient group compared with the control group. B-cell numbers did not change significantly. The decrease of the T-cell count was accompanied by an increase of the null-cell number in patient groups. The levamisole treatment "in vitro' produced an increase in the active-T and total T-lymphocyte counts and led to the decrease of null-cell numbers. These data confirm the available evidence that levamisole "in vitro' may induce the maturation of immature T-lymphocytes in SLE.