We studied peripheral blood mononuclear cells (PBMC) from 34 multiple sclerosis (MS) patients: 8 had chronic progressive (CP) and 26 with a relapsing-remitting (RR) course. PBMC were tested with a panel of monoclonal antibodies (MoAbs) including anti-CD3, CD4, CD8, CD25 reagents. In addition, the suppressor inducer lymphocyte subset was investigated by using two color staining with anti-CD4 and G1-15 and/or anti-CD4 and anti-Leu-8 MoaAbs. A significant decrease of the suppressor inducer subset was found in the exacerbation phase of the RR form. Furthermore, a significant decrease of CD8+ (suppressor/cytotoxic) cells was shown in the remission phase of the RR group. Finally, CD25+ lymphocytes were significantly increased in both phases of RR form.