Eosinophilia-myalgia syndrome (EMS) is a newly recognized disorder, characterized by myalgia, weakness, scleroderma-like changes, and eosinophilia. EMS is associated with lots of L-tryptophan allegedly contaminated with byproducts of the manufacturing process. We describe 3 patients with EMS who presented with a severe demyelinating sensorimotor polyneuropathy. Electrodiagnostic studies revealed multifocal conduction block, slowing and temporal dispersion of motor responses, and prolonged or absent F-responses. Despite plasmapheresis; corticosteroids; and, in 1 patient, cyclophosphamide, 2 patients died and the remaining patient experienced minimal recovery. Pathology revealed patchy perivascular infiltrates and fibrosis in the connective tissue of muscle and nerve. Autopsy of the central nervous system in 2 patients did not reveal changes unique to EMS. In addition to other organ involvement, EMS may manifest as a potentially fatal polyneuropathy, which initially appears to have prominent demyelinating features.