In the routine testing of foods for Salmonella, Citrobacter and other members of the Enterobacteriaceae often produce colonies which are almost indistinguishable from Salmonella on commonly used selective agars. Biochemical confirmation of such colonies can be expensive and timeâconsuming. It has been suggested that the enzyme pyrrolidonyl peptidase (PYRase) could be used as a rapid test to distinguish Citrobacter colonies (PYRaseâpositive) from Salmonella (PYRaseânegative). Pure cultures of Salmonella, Citrobacter and other Enterobacteriaceae were tested for PYRase activity; all strains of Salmonella tested were PYRaseânegative, and all Citrobacter tested were PYRaseâpositive. Inoculated and naturally contaminated food samples were tested for the presence of Salmonella by a standard cultural method. A PYR test was used to test Salmonellaâlike colonies isolated on selective agar and potentially, eliminate PYRâpositive isolates from further biochemical testing. The test was able to screen out 6% of colonies selected from samples inoculated with Salmonella, and 43% of colonies selected from uninoculated samples.