A detailed restriction map of a 430-kb contig comprising the single Ckappa, the 5 Jkappa and the adjoining 22 Vkappa gene segments is presented. The first 12 Vkappa genes following the JkappaCkappa region belong to the Vkappa21 family, the subsequent ones to the closely related families Vkappa8 and Vkappal 9/ 28. Previous difficulties in cloning all Vkappa21 genes can now be explained by the presence of a duplicated region in this part of the locus. The structure was established by analysis of yeast artificial chromosome, bacterial artificial chromosome and cosmid clones and by the so-called long template PCR technique. The distance between Ckappa and the proximal Vkappa21 gene is 22 kb and the average distances between the Vkappa genes are about 20 kb. Of the 12 Vkappa21 genes 5 were sequenced for the first time and 8 of the 12 genes were found to be expressed. Of the 10 Vkappa8 and Vkappa19/28 germline genes 9 are new; expression products of 8 of the 10 genes were known. The known 5', 3' polarities allow to specify for the 22 Vkappa genes whether they are rearranged to the JkappaCkappa element by a deletion or an inversion mechanism. Also the formation of interesting rearrangement products in classical cell lines as MPC11, MOPC41 and PC 7043 can be explained now. The non-Vkappa sequence L10 whose rearrangement by inversion has been described earlier (Hoechtl and Zachau, Nature 1983. 302: 260-263) was now localized downstream of JkappaCkappa.