We examined the changes in the proportions of certain T cell subsets in 18 Guillain-Barré syndrome patients treated with plasmapheresis (PP). PP was performed within 8 days after the onset using a continuous-flow blood cell separator or immunoadsorption. The proportions of CD3+, CD4+ and CD4+CD45RA+ cells at the onset were decreased and that of CD19+ was increased compared with those of 25 normal controls. However, the proportions of CD4+CD45R–, CD4+HLADR+, CD4+CD25+ cells and the CD8+ subpopulations were similar in patients and controls. After PP, the altered subsets tended to normalize, particularly in the group that improved after PP.