The importance of microbial contamination of cadaver kidneys was assessed in 83 consecutively stored and transplanted kidneys. Fourteen kidneys had a single positive culture during storage and five had multiple positive cultures. Only one postoperative infection could be traced to kidney contamination during storage (Candida wound infection). In three of 64 patients who received noncontaminated kidneys, posttransplant wound infections developed. No wound infections occurred in 35 patients who received prophylactic antibiotics, whereas four wound infections occurred in 48 patients without antibiotic coverage. It is concluded that, although microbial contamination of stored cadaver kidneys occurs commonly, it is not an important source of infection in renal transplant recipients.