Two types of chromosomal abnormality have been found in Burkitt's lymphoma-leukaemia. Three specific translocations, t(8;14), t(8;22) and t(2;8), having in common 8q24 band involvement, are thought to be present in the overwhelming majority of cases. These stereotyped translocations have been shown in many cases to be related to DNA molecular rearrangements of the immunoglobulin genes and the c-myc oncogene. Secondary chromosomal abnormalities, some of them nonrandom, have also been described. Their possible relation to other oncogene involvement and to the Epstein-Barr virus genome is discussed.