The prevalence of the enterotoxin gene in a well-characterized collection of 71 Clostridium perfringens strains from 36 separate food-poisoning cases or outbreaks was analyzed with the polymerase chain reaction (PCR). The clonality of 39 strains originating from 14 outbreaks where at least two isolates were available was studied with pulsed-field gel electrophoresis (PFGE) using SmaI and ApaI restriction endonucleases. The cpe gene PCR assay was found to correlate well with Clostridium perfringens enterotoxin (CPE) production in vitro with reverse passive latex agglutination. Of the C. perfringens food and clinical food-poisoning isolates 24 (86%) and 38 (88%) were cpe-positive, respectively. Different PFGE patterns indicated that multiple cpe-positive clones are frequently present within one outbreak. The existence of cpe-positive and negative isolates with identical or nearly identical PFGE patterns in a single outbreak suggests that the cpe gene may be in a movable genetic element.