The 5' region of the mouse kappa locus comprises 63 Vkappa genes in six contigs of together 1.5 Mb, including one which links the region to the central part of the locus. The structures of the contigs were established by detailed restriction mapping of cosmid clones prepared from libraries of mouse C57BL/6 DNA and of yeast and bacterial artificial chromosomes (YACs, BACs with mouse DNA inserts). Pulsed-field gel electrophoresis of yeast artificial chromosome digests indicated that the gaps between the contigs were 10 to 60 kb, comprising together about 160 kb. The region of the kappa locus described here contains Vkappa1, Vkappa2, Vkappa9/10, Vkappa11, Vkappa12/13, Vkappa20, Vkappa24, Vkappa32, Vkappa33/34 and Vkappa38C genes as well as the VkappaRF gene and, towards the center of the locus, a number of Vkappa4/5 genes. Near the 5' end of the locus interspersed alpha-tubulin gene-like sequences were found. At its 3' side the region borders on the Vkappa4/5 contigs of the central region of the locus which is described in the accompanying report (Eur. J. Immunol. 1999. 29: 2057-2064). Structural details are to be found in the Internet at http://www.med.uni-muenchen.de/biochemie/zach au/kappa.htm. In a concluding section the main features of the structure of the mouse kappa locus are summarized.