The authors used plasmapheresis to treat 8 patients with myasthenia gravis and 26 with polyradiculoneuropathy. In myasthenia the treatment was effective in 85% of the cases, as reported in other studies. Good results occurred in some 80% of the cases with acute and relapsing polyradiculoneuropathy. In all cases plasma-exchange was started in the early stage. In chronic polyradiculoneuropathy the treatment was less effective. The authors discuss the advantages, disadvantages and prospects of this kind of therapy.