['The objective of this study is to characterise the functionally relevant minor lymphocyte subpopulations in whole blood of multiple sclerosis (MS) patients and their potential utility as biomarkers for treatment follow up.', 'Peripheral blood from 40 healthy donors (HD) and 66 MS patients [23 relapsing-remitting (RRMS) without treatment, 27 RRMS undergoing treatment (16 IFN-β, 11 natalizumab), and 16 progressive forms (eight secondary progressive and eight primary progressive)] was analysed by multiparametric flow cytometry.', 'Untreated MS patients showed a decrease in early effector memory (CD45RA(-)CCR7(-)CD27(+)) CD4(+) and CD8(+) T cells and an increase in Th17 lymphocytes in peripheral blood compared with HD. Regarding the effect of treatment, whereas no differences in relative percentages of cellular subpopulations were observed in patients under IFN-β treatment, those under treatment with natalizumab had an increased percentage of early effector memory CD4(+) (CD45RA(-)CCR7(-)CD27(+)), central memory CD8(+) (CD45RA(-)CCR7(+)CD27(+)) T cells, recent thymic emigrants (CD4(+) CD45RA(+)CCR7(+)CD27(+)CD31(+)PTK7(+)) and transitional B cells (CD19(+)CD27(-)CD24(hi)CD38(hi)).'] Does multiparametric flow cytometric analysis of whole blood reveal changes in minor lymphocyte subpopulations of multiple sclerosis patients?