A production model of the semi-automated PASCO MIC-ID system (PASCO Laboratories, Wheat Ridge, Colo.) was evaluated with 122 groups or species of gram-negative bacilli, which included typical (499 cultures) and atypical (37 cultures) strains of fermenters and nonfermenters. The PASCO system identified 90.9% of 536 cultures accurately; these included 90.8% of 152 nonfermenters, 93.8% of 308 enteric fermenters, and 78.9% of 76 oxidase-positive fermenters. These results were obtained with the aid of serologic tests and a few additional biochemical tests, when recommended by the PASCO system. Of the 14 misidentified nonfermenters, 3 were Pseudomonas paucimobilis, 3 were Weeksella virosa (Centers for Disease Control group IIf), 2 were Xanthomonas (Pseudomonas) maltophilia, and 6 were randomly distributed among the other groups and species tested. The 19 enteric fermenters that were misidentified were randomly distributed among the groups and species tested. Of the 16 misidentified oxidase-positive fermenters, 4 were Pasteurella ureae, and 12 were randomly distributed among the other groups and species. The system identified the most commonly encountered organisms at a rate of 95% or better. The PASCO system is easy to inoculate and read. A slightly improved data base should remedy most of the identification problems.