Cytofluorographic analysis of CD3+, Tac+, HLA-DR+ peripheral blood lymphocytes and CD4/CD8 ratio was performed monthly, over a 10-month period, in a group of 16 patients with multiple sclerosis (MS). No correlation was found between clinical relapses and fluctuations in the lymphocyte subsets, although patients who were in remission throughout the study showed a number of CD3+ cells and a CD4/CD8 ratio significantly lower than those in normal controls. We concluded that changes in peripheral blood lymphocyte subsets are not related to the disease process and their measurement is not helpful in monitoring the illness.