The identification and susceptibility testing of bacteria by the autoSCAN-W/A rapid panels and Vitek Automicrobic systems were compared. A total of 291 clinical isolates, including 207 members of the Enterobacteriaceae, 41 nonfermentative gram-negative bacilli, 31 Staphylococcus aureus strains and 12 Enterococcus faecalis strains, were tested. autoSCAN-W/A and Vitek correctly identified 93% and 94% respectively of the Enterobacteriaceae, the identification in an additional 2% and 5% of strains respectively being reported as correct with a low probability. autoSCAN-W/A reported all identification results within 2 h after inoculation, whereas Vitek reported the identification results for the majority of gram-negative bacilli between 4 h and 6 h after inoculation. autoSCAN-W/A and Vitek reported 81% and 74% of MIC results respectively after 3-6 h incubation. The rates of very major susceptibility errors were 0.4% and 0.4% for autoSCAN-W/A and Vitek respectively, the rates of major errors 0.4% and 1% respectively, and the rates of minor errors 4% and 3% respectively. Six of 30 Pseudomonas aeruginosa strains failed to grow sufficiently for susceptibility testing in the autoSCAN-W/A system, and four Xanthomonas maltophilia strains had insufficient growth for susceptibility testing in both systems. The majority of results of susceptibility testing of nonfermentative gram-negative bacilli were reported more than 6 h after inoculation. Both systems were reliable and easy to operate, and gave accurate results for common clinical isolates.