Sequences encoding immunoglobulin variable domains are known to be assembled from variable (V), diversity (D), and joining (J) segments by site-specific recombination. We present a sensitive and rapid assay for V-(D) J recombination that uses plasmid DNA transiently introduced into transformed pre-b cells, and demonstrates that the recombination is independent of any unique chromosomal context. Sequences sufficient to constitute recombination sites are contained within the 84 and 42 bp flanking, respectively, the murine J, l and V, L8 segments, which include the known heptamer-nonamer V-(D) J joining signals. Deletion and inversion occur at comparable frequencies. Thus, V-(D) J recombination may be relatively insensitive to the topological arrangement of sites, and events at the two novel junctions produced by the reaction may be coupled.