By comparing the restriction patterns of the DNA from 23 unrelated individuals 16 polymorphisms were defined which allowed us to differentiate between the duplicated copies Op, Ap, Lp and Od, Ad, Ld of the kappa locus (p for the C kappa proximal, d for the distal copy). Some of these duplication-differentiating polymorphisms or DDP revealed also allelic differences between individuals; they are therefore restriction fragment length polymorphism (RFLP) markers at the same time. Three RFLP in the single copy B-J kappa-C kappa region were included into the study. Three basic haplotypes were derived from the combined genotype data, haplotypes N, G and 11. The latter haplotype in which the whole distal copy of the kappa locus is missing was found three times among the 46 haploid genomes studied. The genotypes of the family members of an individual who is homozygous for haplotype 11 are consistent with Mendelian inheritance. Haplotypes N and G are distinguished from each other by eight RFLP markers. Six additional haplotypes, which were found in one or several individuals each, can be derived from the basic haplotypes N and G by hypothetical recombination and/or mutation events.