Out of 4,114 cultures of Salmonella belonging to various serotypes, 1,241 (30,1%) hydrolyze p-nitrophenyl-beta-D-glucuronide, the chromogenic substrate of beta-glucuronidase. Serotypes are found to be homogenous with respect to beta-glucuronidase activity. The qualitative test, as simple as the ONPG test, may be of diagnostic value to assign a strain to a serotype in case of a monophasic or not motile variant of a normally diphasic serotype. Phage conversion does not influence beta-glucuronidase activity.