The scope of this book is to highlight the practical need for distinguishing those Gram-negative bacteria, such as Pseudomonas and Acinetobacter, that oxidize carbohydrates and those that do not utilize carbohydrates, such as Alcaligenes, from members of the family Enter-obacteriaceae which ferment sugar substrates. This chapter is concerned with a practical system for identifying members of the genus Pseudomonas. In diagnostic microbiology, laboratory identification of pseudomonads and other glucose nonfermenting bacteria is based on phenotypic characters including morphological, physiological, and nutritional attributes. Diagnostic tests outlined in this chapteryield a sufficiently broad picture of the phenotypic traits of pseudomonads to permit satisfactory identification of most species encountered in clinical microbiology. Species which share many common properties can be placed in subgeneric or phenotypic groups; the approach here is to discuss these bacteria on the basis of their subgeneric or species grouping, as outlined in Table 1.