A retrospective review of microbiology records revealed 19 documented episodes of M. morganii bacteremia in 18 patients at a Veterans Administration hospital during a 5.5 year period. Thirteen of 19 bacteremias were related to nosocomial infections; 11 of the 13 nosocomial bacteremias occurred in surgical patients. Nine of the 13 patients with nosocomial bacteremia had received recent therapy with a beta-lactam antibiotic. The most common source of bacteremia was a postoperative wound infection (seven episodes). Only one episode was related to a urinary tract infection. Retrospective analysis showed that clusters of cases of M. morganii bacteremia had occurred almost yearly. This finding prompted a six-month period of prospective monitoring of all cultures for M. morganii to identify human reservoirs in our institution. Sixty percent of all cultures growing M. morganii came from urine cultures, 18% came from wound cultures, and the remaining 22% came from a variety of body fluids or tube drainage. Thirty-one percent of patients harboring M. morganii were on the Surgical Service. M. morganii bacteremia most commonly occurs in postoperative patients who receive beta-lactam antibiotics. From the data in this study, M. morganii is an infrequent cause of bacteremia, and its presence in blood cultures may be an indicator of an environment conducive for an outbreak of nosocomial infection.