The present study deals with the characterization of peripheral blood T-cell subpopulations in multiple sclerosis (MS) patients during different stages of the disease. An indirect immunofluorescence assay was performed using monoclonal antibodies directed at lymphocyte surface antigens. Patients in exacerbation were found to have significantly (p less than 0.001) reduced OKT8+ (T-suppressor) cells and a high helper/suppressor ratio (p less than 0.001). Patients in remission showed a significant increase of suppressor T-cells compared to controls (p less than 0.02) and patients during relapse (p less than 0.001); H/S ratio was consequently low compared to acute MS (p less than 0.001) and controls (p less than 0.1). Patients with a progressive course showed an intermediate T-subset pattern. The results are discussed in the light of the most recent neuroimmunological approaches to MS.