During an 18-month period we identified two cases of septicemia and 24 examples of colonization of humans by Klebsiella trevisanii. Organisms were identified using the API 20EC and API 147 assimilation galleries. Of 147 clinical isolates initially identified as K. oxytoca, 18% were found to be K. trevisanii. Tracheal aspirate was the most common source of the organism. An extensive environmental sampling survey in the rooms of 12 colonized patients revealed a possible reservoir of the organism only once (a face cloth).