Two DNA probes for the detection of insertion sequence IS200 by either Southern blotting or colony hybridization were constructed. One of the probes is a 300 bp EcoRI-HindIII fragment of IS200 cloned onto pBluescript KS(+); the other is a tail-to-tail dimer of the same fragment cloned onto pUC19. A survey of the presence of IS200 among enteric bacteria revealed that more than 90% of the pathogenic or food-poisoning isolates of Salmonella spp. examined contained one or more copies of insertion sequence IS200, with the exception of the subgenus I serovar S. agona in which IS200 is not found. Although insertion sequence IS200 was first considered a Salmonella-specific element, it also exists in many isolates of Shigella sonnei and Shigella flexneri, but not in Shigella dysenteriae.