Aberrant immune responses to several unrelated antigens observed in patients with multiple sclerosis have suggested faulty regulation of immunocompetent cells. Recently human T lymphocytes have been segregated into subpopulations. T lymphocytes that bear Fc receptors for IgG suppress B lymphocyte proliferation and the production of IgG. Here we report studies on the percentage of TG cells in the peripheral blood of 25 patients all of whom met stringent clinical criteria for the diagnosis of multiple sclerosis (MS). Many of these patients were followed for more than 14 months. In the total group, nine patients experienced definite acute exacerbations of disease followed by periods of remission. The mean percentages +/- 1 standard deviation of TG cells found in all MS patients during remission, 16 +/- 6 was significantly higher than the mean found in normal subjects, 12 +/- 2. In contrast, the mean found in patients experiencing an acute attack, 6 +/- 2 was significantly lower than the mean TG level of normal subjects. Moreover, when individual patients were followed through their clinical illness, levels of TG lymphocytes that were low during acute exacerbations invariably increased to relatively high levels with the onset of clinical remission.