A simple and rapid semiquantitative slide catalase test useful for the identification of oxidative and nonsaccharolytic gram-negative bacteria, i.e., "nonfermenters," is described. Using the interpretative criterion of time of appearance of oxygen bubbles in 3% hydrogen peroxide, three categories of nonfermenters were established. The rapid catalase producers included Achromobacter xylosoxidans and Achromobacter species; Acinetobacter anitratus and Acinetobacter lwoffii; Bordetella bronchiseptica; CDC group IVE; Pseudomonas aeruginosa, P. fluorescens, P. putida, P. diminuta, and P. acidovorans; and Moraxella urethralis and M-6. The delayed catalase producers included Bordetella parapertussis, CDC group VA-1, P. alcaligenes, P. cepacia, P. mendocina, P. pickettii (VA-2), P. pseudoalcaligenes, P. putrefaciens, P. stutzeri, P. testosteroni, and P. vesicularis. The third group consisted of an additional 17 taxa of nonfermenters which were classified as moderate catalase producers.