The Clostridium perfringens enterotoxin gene (cpe) is rarely found in naturally isolated strains. In human food poisoning strains, cpe is found on the chromosome, and is located episomally in animal isolates. Observations that the gene was somewhat unstable and could be gained or lost suggested that the gene was on a mobile element. An IS200-like element, IS1469, is almost always upstream of cpe. A new insertion element was identified, IS1470, a member of the IS30 family, which is found both up-an downstream of cpe in the type A strain NCTC 8239. PCR results confirmed that this configuration was conserved in type A human food poisoning strains. The enterotoxin gene was on a 6.3 kb transposon which, in addition to the two flanking copies of IS1470, included IS1469 and two 1 kb stretches, one on each side of cpe, with no open reading frames. Results indicated that 14 bp was copied from the genome during insertion. Details of the configuration of DNA in this transposon are presented, and the possible connection of this transposon with the movement of the enterotoxin gene is discussed.