The API 20 NE system is designed for the rapid identification of Gram negative rods other than Enterobacteriaceae. It has been compared to conventional methods in the characterization of 404 strains representative of 23 species belonging to 3 genera: Pseudomonas (236 strains), Flavobacterium (133 strains) and Alcaligenes (35 strains). The system consists of 9 enzymatic tests and 12 carbohydrate assimilation tests. A 7-digit numerical profile is obtained by an octal coding of the test results. The strains are identified by comparing the numerical profile to those of species listed in a profile index. The API 20 NE tests showed 99-100% correlation with corresponding conventional methods except in indole production (96.5%) for which we observed 14 false negative reactions in testing F. meningosepticum and CDC groups IIb and IIf. The API 20 NE system presented 94.1% identification to the species level and 96.3% to the genus level in agreement with conventional biochemical methods. Among the correctly identified strains, 7.4% (30) gave an erroneous or unlisted numerical profile in the first version of the Profile Index and required the use of the computer. Among the misidentified strains 2%, (8) were assigned to the right genus but wrong species, 0.7% (3) were placed in the wrong genus and 1% (4) gave a doubtful profile with one or more tests compared to the profiles listed.