Tetrathionate reduction can be detected simply by acid production. Some commonly occuring Salmonella serotypes can be subdivided into biotypes by the tetrathionate reductase test. The enzyme beta-glucuronidase can be detected using p-nitro-phenyl-beta-D-glucuronide as substrate. The enzyme was found in 30% of Salmonella strains. Each Salmonella serotype was found homogeneous with respect to presence of (or lack of) beta-glucuronidase. This test can then be useful for the identification of monophasic or non-motile variants of normally diphasic serotypes. A positive ONPG-test does not always indicate the presence of a true beta-galactosidase. In the genus Salmonella, ONPG-positive strains of sub-genus III and strains harboring a lactose-plasmid have a true beta-galactosidase. A late positive ONPG-test - as commonly shown by subgenus II strains - is not due to a true beta-galactosidase. The distinction between beta-galactosidase positive and beta-galactosidase negative strains among ONPG-positive strains may be taxonomically significant.