The ability of a rapid, semiautomated bacterial identification system, the Quantum II microbiology system (Abbott Laboratories, Irving, Tex.), to accurately identify gram-negative bacteria from veterinary sources was evaluated. A total of 378 isolates were tested, including 298 organisms in the family Enterobacteriaceae and strains representing Acinetobacter sp., Aeromonas sp., Flavobacterium sp., Pasteurella multocida, Plesiomonas sp., and Pseudomonas spp. Of these isolates, 333 (88.1%) were correctly identified, 20 (5.3%) were not identified, 10 (2.6%) were incorrectly identified at the genus level, and 15 (4.0%) were incorrectly identified at the species level. The Quantum II system correctly identified 268 (89.9%) of the isolates of Enterobacteriaceae and 65 (81.3%) of the nonenteric isolates. P. multocida was not identified correctly, and some nonenteric gram-negative bacteria of clinical significance in veterinary medicine are not included in the data base. The Quantum II system provided an accurate identification system for isolates of Enterobacteriaceae but had limited usefulness for the identification of other gram-negative bacteria of clinical significance in veterinary medicine.