Two rare cases of chronic lymphocytic leukemia (CLL) in children, patients AS and LH, have been found to be associated with a unique chromosomal translocation, t(2;14)(p13;q32). Previous studies have shown the breakpoints of this translocation to be in the gamma 2 switch region of the Ig heavy-chain locus on chromosome 14 and in an uncharacterized region of chromosome 2. We have cloned and characterized the translocation breakpoints to examine the possibility that an oncogene contributed to the pathogenesis of these cases of CLL. Sequence analysis of AS and LH breakpoints established that the chromosome 2 breakage in the two patients occurred only 38 bp apart and within a strong non-methylated CpG island. Furthermore, human probes from the region cross-hybridized to other species, indicating strong evolutionary conservation. Northern analysis using the chromosome 2 probes detected a 2.85-kb transcript in the tumor cells and in a CD5+ B-cell line. These data suggest that a potential oncogene located near the 2p13 breakpoint may have been activated by the t(2;14) translocation in these two cases of chronic lymphocytic leukemia.