Peripheral blood T and B lymphocytes were enumerated using E and EAC red blood cell rosetting techniques. The percentage of EAC-binding cells in peripheral blood of multiple sclerosis patients is elevated (31.7 ± 2.4 S.E.M.) when compared with the percentage in healthy controls (18.5 ± 1.1 S.E.M.). The total T cell percentage is not significantly lower in multiple sclerosis than in controls, but fewer T cells in patients with multiple sclerosis are able to bind 10 or more red blood cells.