A patient with Guillain-Barré syndrome was successfully treated by plasma exchange (without any other therapy), and the relationship between changes in his peripheral blood lymphocyte subpopulations and the clinical improvement induced by plasmapheresis was studied. At the recovery, the most interesting findings were an increase in T suppressor lymphocytes, and in Fc receptor-bearing lymphocytes (above normal values), together with a decrease in B lymphocytes. In this patient, plasma exchange not only removed toxic humoral factors, but also restored a normal balance among peripheral lymphocytes.