A heat-labile enterotoxin and no heat-stable enterotoxin producing($LT^+ST^-$) plasmid (110 kilobases in size) was isolated from an enterotoxigenic Escherichia coli of human strain O15:H11 and used for analysis of the $LT^+$ deoxyrionucleic acid region using recombinant DNA technology. A DNA segment containing the $LT^+$ DNA region which was one restriction endonuclease BamHl fragment(6.2 kb in size) was joind to a small multicopy plasmid, pUC9. E. coli K-12 strain, JM103 harboring the chimeric plasmid produced greater amounts of LT than did the enterotoxigenic E. coli O15:H11 strain. The BamHl fragment was further digested with various restriction endonucleases and contained no HindIll restriction site which is an essential in $LT^+ST^+$ plasmid. The detailed DNA sequencing of this $LT^+ST^-$ plasmid is required.