The immunoglobulin kappa genes of nonhuman primates were studied by using sequence information and hybridization probes derived from the human kappa gene regions. The following results were obtained: (1) V kappa gene probes of the three major human kappa subgroups hybridized to restriction nuclease digests of DNA from the chimpanzees Pan troglodytes (PTR) and Pan paniscus (PPA), the gorilla Gorilla gorilla (GGO), the orangutan Pongo pygmaeus (PPY), the macaque Macaca mulatta (MMU), the marmoset Callithrix geoffrei (CGE), and the bushbaby Galago demidovii (GDE), yielding patterns of decreasing similarity to the patterns of the human V kappa multigene family. (2) The C kappa gene segments of PTR, GGO, and PPY were 99.6, 97, and 93%, respectively, identical in sequence to the human C kappa gene. A V kappa gene in PTR, GGO, PPY, and MMU was 98, 96, 96, and 95%, respectively, identical to the most C kappa proximal V kappa gene, called B3. The other two J kappa-C kappa proximal V kappa genes in human, B1 and B2, hybridize to restriction fragments of sizes identical to that of DNA from humans and great apes. (3) The long-range restriction maps of the human (HSA), PTR, and GGO kappa loci as established by pulsed-field gel electrophoresis (PFGE) are quite homologous. According to the maps, however, and to hybridization studies with 11 duplication-differentiating probes, there is only one copy of the locus in PTR and GGO. This means that the duplication of large parts of the kappa locus as found in humans occurred after the branch-point of human and great ape evolution.(ABSTRACT TRUNCATED AT 250 WORDS)