Southern blot analysis of four typical and four aggressive mantle cell lymphomas. HindIII-digested DNA was electrophoresed on a 0.8% agarose gel, transferred to a nylon membrane, and hybridized with the exon 2 of p16^INK4a, p21^Waf1, and bcl-1 MTC probes. The aggressive MCL 3858 and 15566 show homozygous deletions of p16^INK4a and p15^INK4b genes. No alterations in the p21^Waf1 signal was seen in any of the cases. Case 4958 had a bcl-1 rearrangement detected with HindIII. Case 441 also had a bcl-1 rearrangement detected with EcoRI and BamHI but not with HindIII. No rearrangements were detected in the remaining cases.