Clinicopathological studies were performed on the visceral organs and the sural nerve of a male patient with Churg-Strauss syndrome (CSS) in order to understand the mechanisms of peripheral nervous system damage. A 67-year-old man, with a 2-year history of bronchial asthma, developed acutely painful paraplegia and dyspnea. Laboratory data showed a leukocytosis, an elevated serum creatinine kinase (CK) and marked eosionophilia. Autoantibodies including p- and c-ANCA were negative. Electrophysiological studies revealed a severe sensory-motor neuropathy of multiple mononeuritis type. Steroid pulse therapy performed a day after biopsy of skin, muscle and sural nerve was effective in resolving his respiratory and neurological dysfunction but a perforation of an intestinal ulcer occurred which required surgical intervention. In the biopsied sural nerve and the surgically resected intestine and mesentery there was vasculitis with fibrinoid necrosis accompanied by numerous eosinophils and macrophages containing eosinophil cationic protein (ECP). These findings suggest that in addition to ischemic changes due to vasculitis some neurotoxic substances generated by the eosinophils may be involved in the development of neuropathy in CSS.