The API-20 Enteric Strip has been proposed to have the capacity to differentiate the nonfermentative gram-negative bacilli. This multitest strip serves as the basis of an evolving system, which first provided a Register, then a Selector, and more recently a computer Index. Twenty-three strains of Pseudomonas aeruginosa and P. putida, 21 of P. fluorescens, 27 of P. maltophilia, and 33 of P. cepacia were investigated by duplicate test runs to determine reproducibility. The results were then evaluated at each of the three stages to determine accuracy of identification and the effect of the system evolution on the identification rate. Seventy-one of the 127 pseudomonads gave reproducible results in the multitest strips. Approximately half of them were correctly grouped or speciated by the Register, whereas 80 to 83% were similarly identified by both the Selector and Index. Of the clinically important pseudomonads, 61 to 65% of P. aeruginosa and 93% of P. maltophilia strains were correctly speciated; neither P. putida nor P. fluorescens strains were speciated, although most were correctly grouped. P. cepacia was speciated by the Index with only 55 to 58% accuracy. Although the present stage of the evolving system offers improvement over the Register, further modifications are needed to eliminate identification problems and to increase speciation.