The study--on continuous cell lines or on fresh tumor cells--of chromosomes and immunoglobulins from 29 Burkitt-type lymphomas or leukemias showed a strong correlation between translocation t (2; 8) and expression of kappa light chains on the one hand, and between translocation t (8; 22) and expression of lambda chains on the other. The positions of the genes that code for these immunoglobulin chains, on chromosomes 2 and 22, respectively, suggest a precise regional localization close to the break-points observed in the translocations (2p12 and 22q11). These results should make it possible to look for and identify the DNA sequences that are implicated in the malignant transformation of these cells, using molecular biology techniques.