Described here is a simple polymerase chain reaction (PCR) method for detecting rearrangements involving the bcl-2 gene. Rearrangements in bcl-2 are characteristic of follicular B-cell lymphoma (present in >80% of cases) and can occur in other malignancies (refs. 1 –5 ; see review of bcl-2 in ref. 6 ). Tumors with these rearrangements usually have a chromosome translocation [t(14; 18) (q32;21)] that places bcl-2 (normally on chromosome 18) adjacent to the joining region (JH ) of the immunoglobulin heavy chain locus (normally on chromosome 14). The translocation results in a high level of expression of bcl-2 , presumably due to the proximity of enhancers within the immunoglobulin locus (7 ), The translocation breakpoint in bcl-2 usually lies downstream of the protein coding region in one of two regions termed the major breakpoint region (MBR) and the minor cluster region (MCR). The MBR is in the 3′-untranslated region of bcl-2 ; approx 50–60% of breakpoints occur within this R~150 bp region (8 ,9 ). The MCR is in 3′-flanking genomic DNA about 20 kb 3′ of the MBR (8 ); approx 10–25% of breakpoints occur within this R~500 bp region (8 ,9 ).