Chromosome 11q13 translocation breakpoints have been found dispersed over more than 100 kb of genomic DNA in centrocytic lymphoma and lymphocytic lymphoma of intermediate differentiation (mantle cell lymphoma). Approximately one-half of these translocations occur at the bcl-1 major translocation cluster (MTC) and appear tightly clustered by Southern blot restriction mapping. In order to specifically characterize these t(11;14)(q13;q32) translocations, six cases of centrocytic lymphoma with MTC rearrangements on Southern blot were studied. Genomic DNA was amplified by PCR (polymerase chain reaction) using a consensus immunoglobulin heavy-chain joining gene (JH) primer and two separate MTC primers. Sequencing of the PCR products revealed the MTC breakpoints in all six cases to be clustered within a 61 basepair span, very similar to those previously reported in t(11;14)-containing human B-cell lines. No two breakpoints were identical. JH breakpoints involved JH4 in five cases and JH6 in the other. Tight clustering of the MTC breakpoints thus permits PCR detection of the t(11;14) in many cases of centrocytic lymphoma, which may be of value in classifying this subtype of non-Hodgkin's lymphoma.