Transcriptional regulatory elements have been shown to be necessary but not sufficient for the developmental regulation of immunoglobulin gene rearrangement in mouse precursor B cells. In the chicken lambda light chain locus, additional elements in the V-J intervening sequence are involved in negative and positive regulation of rearrangement. Here, mutation of the mouse homolog of a chicken element, located in the V-kappa-J(kappa) intervening sequence upstream of the J(kappa) duster, was shown to significantly decrease rearrangement. This cis-acting recombination-enhancing element affects the rearrangement process without being involved in regulating transcription.