We present a patient with polymicrobial endocarditis who had been operated on previously for a mycotic aneurysm and was seen at the cardiology clinic because of palpitations related to effort. A transesophageal echocardiogram revealed a 15-mm vegetation on his aortic valve. Staphylococcus epidermidis and Corynebacterium striatum were isolated from the blood cultures. Both strains were multiresistant (susceptible to 3 antibiotics at most) against chemotherapy in vitro. Microbiological eradication was not achieved from blood cultures even after applying antimicrobial therapy with effective antibiotics as determined with an antibiotic susceptibility test. For this reason, the patient underwent valve replacement. He was discharged from hospital in fairly good health. Copyright (C) 2002 S. Karger AG, Basel.