Chromosomal translocations are found to be a characteristic feature of Burkitt lymphomas. Similar translocations are found in mouse plasmacytomas and both diseases involve interchanges between one of the immunoglobulin loci and DNA in the vicinity of the myc gene. The structure of the myc gene has been elucidated from studies on translocated versions of the gene. Activation of the myc gene may play a role in transformation by promoting growth of the cells bearing the rearranged chromosomes.