The chromosomal breakpoint involved in the t(8;14)(q24;q11) chromosome translocation in the SKW-3 cell line, which directly involves the 3′ flanking region of the c-myc gene, was cloned and sequenced. The breakpoint on chromosome 8 mapped to a position 3 kb 3′ of c-myc while the chromosome 14 breakpoint occurred 36 kb 5′ of the gene for the constant region of the α chain of the T-cell receptor (TCR). The translocation resulted in a precise rearrangement of sequences on chromosome 8 and what appears to be a functional J_α segment on chromosome 14. Signal sequences for V-J joining occurred at the breakpoint positions on both chromosomes 14 and 8, suggesting that the translocation occurs during TCR gene rearrangement and that it is catalyzed by the enzymatic systems involved in V-J joining reactions. The involvement of c-myc in the translocation and the association of joining signals at the breakpoints provides a parallel to the situation observed in the translocations involving c-myc and the immunoglobulin loci in B-cell neoplasms and suggests that common mechanisms of translocation and oncogene deregulation are involved in B- and T-cell malignancies.