We have analyzed the structure of Ig kappa chain genes in B cell lines derived from a human individual who cannot synthesize any kappa chains, and whose Igs all contain lambda chains (1). We have characterized secondary DNA recombination events at two kappa alleles which have undergone misaligned V-J recombinations. One such secondary recombination has joined the flanking sequences of a V kappa and a J kappa 2 gene segment as if it were the reciprocal product of a V-J kappa 2 recombination, and resulted in the displacement of the recombined VJ kappa 1 gene segments from the C kappa locus. The non-rearranged form of the V kappa fragment which had recombined with the J kappa 2 flank was cloned. Nucleotide sequencing of this fragment identified a V kappa gene that differed by at least 38% from all previously sequenced human V kappa genes. The other V-J kappa segment analyzed has undergone a secondary recombination at a different site from that described above, at a site within the intervening sequence between the J kappa and C kappa gene segments, similar to the location of secondary recombinations which have occurred in lambda + B cell lines from mice and humans (2,3). These results prove that multiple recombinations can occur at one J kappa-C kappa locus.