Helper-inducer (CD29+CD4+) and suppressor-inducer (CD45RACD4+) T-cells have been recently renamed as memory and naive T-cells, respectively. We measured cells expressing these phenotypes in peripheral blood of 46 definite multiple sclerosis (MS) patients [32 relapsing-remitting (RR-MS), 14 secondary progressive (P-MS)] and controls. CD25+ (interleukin-2-receptor-positive) cells were also evaluated in the same groups of patients. RR-MS patients showed increased levels of CD29+CD4+ and CD25+ cells compared with controls. This finding was more evident in RR-MS patients during the attack than during the stable phase of the disease. In P-MS patients we found a reduction of CD45+CD4+ cells compared with either RR-MS patients or control subjects. Our results show that RR-MS and P-MS are characterized by two different T-cell subpopulations. This finding supports the hypothesis that during the evolution from RR-MS and P-MS changes occur in the immunological status of the patients.