We analyzed peripheral blood and CSF T-cell subsets in Japanese patients with MS, using an OK series of monoclonal antibodies in an immunofluorescent techniaue. In the Peripheral blood, suppressor. T cells were increased, with a concomitant decrease in helper T cells, after recovery from acute exacerbation, but there was no relationship between T cells in peripheral blood and CSF. In the CSF, acute exacerbation was associated with an increase in Ia-positive cells and a decrease in T cells. CSF pleocytosis (with more than 30% of Ia-positive cells) probably indicated active disease.