A DNA segment originally found in an epidemic plasmid of Escherichia coli encoding an aminoglycoside-(3)-N-acetyltransferase gene (aacC5) and a TEM-type beta-lactamase gene was characterized. The two genes were adjacent and constituted a single transcriptional unit. In addition, these genes were simultaneously mobilized through the action of an insertion sequence related to IS26, IS140, and IS15-delta. This DNA segment is a composite transposon which has been called Tn2922.