In 3 patients with subacute polymyositis, muscle biopsies were remarkable for showing abundant infiltration by eosinophils. In each case the inflammatory myopathy was part of a systemic illness known as the hypereosinophilic syndrome (HES). The systemic manifestations included eosinophilia, anemia, hypergammaglobulinemia, vascular involvement (subungual petechiae, livedo reticularis, Raynaud's phenomenon), skin rash and subcutaneous edema, pulmonary infiltrates and pleuritis, cardiac involvement (congestive heart failure, arrhythmias, heart block, pericarditis, myocardial and endocardial fibrosis), and peripheral neuropathy. Myopathy has received scant mention in previous reports of HES, but 30% of the patients had neurological symptoms such as encephalopathy, multiple cerebral infarcts (possibly embolic in origin), peripheral neuropathy, and mononeuropathy multiplex. The prognosis is poor, average survival being only nine months after the onset of symptoms; but 2 of our patients, and a few reported by others, have responded well to corticosteroid treatment.