In situ hybridization studies were performed on two Burkitt lymphoma cell lines with variant t(2;8) translocation. In both cell lines the Ck-gene is found in juxtaposition to the c-myc gene on the 8q+ chromosome. The location of the c-myc gene 5' of an immunoglobulin constant gene appears to be a general feature of all Burkitt lymphomas. On the 2p chromosome the site of the breakpoint of the translocation is variable. In the cell line BL 64 the break is in the fragment carrying Jk sequences and in cell line JI it is between Jk and Vk. In the cell line BL 64 different marker chromosomes were observed which result from breakage near or within the JGK-gene cluster on chromosome 2p.