The capability of the Auto-Microbic system (Vitek Systems, Inc., Hazelwood, Mo.) has been expanded to identify members of the family Enterobacteriaceae with the use of a sealed, disposable accessory card (the Enterobacteriaceae Biochemical Card) containing 26 biochemical tests. To judge the accuracy of the AutoMicrobic system's identification in a hospital laboratory, 933 Enterobacteriaceae isolates were studied. The AutoMicrobic system provided the correct identification for 905 of the isolates (97%). For Enterobacteriaceae excluding Escherichia coli (533 isolates not E. coli), 506 isolates were correctly identified (94.9%). The AutoMicrobic system integrates well into the clinical microbiology laboratory, providing a simple, accurate, and efficient automated system for the rapid identification of Enterobacteriaceae.