The AA. report the results obtained with Plasma Exchange (P.E.) therapy on 24 cases of polyradiculoneuritis; eleven patients had typical Guillain-Barré Syndrome (G.B.S.) ten suffered from a chronic progressive form and three were affected by a relapsing form. The acute patients were selected according to criteria established by the NNCDS Committee (1978) while guidelines laid down by Pineas & Load (1978) were followed in choosing chronic cases. Patients with G.B.S. had four sessions of P.E. at intervals of one or two days while those with chronic forms of polyradiculoneuritis had a total of 6 sessions spaced one to three days apart. P.E. produced no apparent change in chronic progressive patients but two out of three cases with the chronic relapsing form showed rapid and steady improvement resulting in complete cure within a few months. Nine of the eleven G.B.S. patients showed after only one or two sessions a clear and rapid improvement which led to a complete cure within a matter of weeks. The remaining 2 cases showed only partial improvement at first and remained stationary thereafter. The findings confirm the usefulness of P.E. in acute and chronic relapsing radiculopolyneuritis. However, potential side effects and the procedure's high cost suggest that its use should be limited to carefully selected cases, and in particular to those involving respiratory disorders.