The nucleotide sequence of the 1494 bp wxB4 Ds element is presented. A comparison with previously characterized Ds elements reveals several novel features. This element has less Ac terminal sequence than other Ac-like Ds elements. The left terminus contains 398 bp of Ac sequence interrupted by a transposon-like DNA insertion, leaving only 317 bp of contiguous Ac sequence. The right terminus has 259 bp of Ac terminal sequence. The interior of the element contains sequences not found in other cloned members of the Ac/Ds family. We suggest that the role of this non-Ac DNA is to separate the Ac termini by a minimum distance and may be a cis requirement for Ds transposition in maize.