Recent molecular analyses of Burkitt lymphomas carrying the t(8;14) chromosome translocation have indicated that a dichotomy exists regarding the molecular mechanisms by which the translocations occur. Most sporadic Burkitt tumors carry translocations that apparently arise due to mistakes in the immunoglobulin isotype-switching process. In contrast, there is evidence that the translocations of most endemic Burkitt lymphomas occur as a consequence of aberrant V-D-J recombination of variable, diversity, and joining gene segments, catalyzed by the recombinase enzymes. This phenomenon was first noted in follicular lymphomas and chronic lymphocytic leukemias of the B-cell lineage and has been described in T-cell malignancies as well. In each of these cases, analysis of the nucleotide sequence at chromosome breakpoints demonstrated the involvement of immunoglobulin heavy chain JH or T-cell-receptor alpha-chain J alpha gene segments in the translocation. We now have cloned and sequenced both the 8q- and 14q+ translocation breakpoints deriving from the t(8;14) translocation of the endemic Burkitt lymphoma line Daudi. Our data show that the translocation resulted from a reciprocal exchange between the DH region on chromosome 14 and sequences far 5' of the MYC protooncogene on chromosome 8. Features of the nucleotide sequences surrounding the breakpoint further implicate the V-D-J joining machinery in the genesis of chromosome translocations in endemic Burkitt lymphomas and, more generally, in other lymphoid malignancies as well.