Translocations involving chromosomes 8 and 14 in Burkitt's lymphoma (BL) often involve the switch mu (Smu) region on chromosome 14, which contains multiple repeats. This has enabled us to use the polymerase chain reaction (PCR) to detect breakpoints that involve this region on chromosome 14 and the c-myc gene on chromosome 8. Using pairs of flanking primers, each pair including one annealing to repeat sequences within the switch region and one of three primers from the c-myc region (first intron, 3′, or 5′ flanking sequence of the first exon of c-myc), we have been able to amplify DNA fragments containing the corresponding breakpoint regions from chromosome 14 in both cell lines and biopsied tumor samples. The definitive demonstration of sequences from both chromosomes in these fragments permitted the confirmation of the presence of a translocation. Because of the sensitivity of PCR, we were able to localize breakpoints in samples containing as few as 1 neoplastic cell in 10(8) cells. PCR provides a valuable tool for the detection of 8;14 chromosomal translocations, which should prove to be of value in diagnosis and molecular epidemiologic studies, as well as providing a means of detecting minimal disease.