An adult man presented severely ill with vasculitis of his lower extremities and with impaired kidney function. After detailed evaluation at a local hospital, a diagnosis of essential type III cryoglobulinemia was made. High-dose steroid and cyclophosphamide therapy was begun. The patient improved dramatically. However, 6 wk later when his steroid dose was reduced to 30 mg daily, vasculitis recurred. Intensifying his immunosuppressive therapy only worsened his condition. He was than transferred to the Ohio State University Medical Center for consideration for plasmapheresis for the presumed essential type III cryoglobulinemia. However, our evaluation showed that he had bacterial endocarditis causing his type III cryoglobulinemia. When immunosuppressive drugs were stopped and antibiotics were begun, his condition resolved completely. This case illustrates the difficulty of identifying infectious causes of cryoglobulinemia and emphasizes that an initial, highly favorable response of vasculitis to immunosuppressive therapy does not exclude an infectious cause for the vasculitis.