The element which mediates the deletion of the CK gene segment (abbreviations ref. 1) in human lambda light chain producing B-cells was found to be located 24 kb downstream of CK. The kappa deleting element is flanked by hepta- and nonanucleotide recognition sequences similar to the ones adjacent to the JK gene segments. Complementary recognition sequences with a 30 bp spacer were found in the JK-CK intron. For the first time the two partners of a recombination event in a mammalian immunoglobulin gene system have been linked on a physical map. The orientation of the recombination signals of the intron and the Kde sequences allows a joining by a simple deletion mechanism. Similarities and possible differences to the mechanism of V-J joining are discussed.