The molecular genetic hallmark of mantle cell lymphomas (MCL) is the reciprocal translocation t(11;14)(q13;q32) which juxtaposes the bcl-1 proto-oncogene to one of the joining segments of the immunoglobulin heavy chain gene. This translocation is very common in MCL and occurs in up to 70% of these malignancies. Due to the aggressive nature of MCL, markers identifying tumor progression and clinical outcomes are necessary. In this study we examined whether a corroborative relation exists between p53 mutations, bcl-1 translocation, and the proliferative fraction in MCL. We evaluated the proliferative fraction, p53 gene status, and bcl-1 translocation in 21 patients with confirmed MCL. Controls consisted of normal DNA and 7 B-cell lymphomas. Immunohistochemical detection of Ki-67 was used to assess proliferative activity while molecular techniques were used to detect p53 mutations and the bcl-1 gene translocation. Reactivity to the monoclonal antibody Ki-67 on neoplastic cells ranged from 5% to 40% in typical MCL cases. The bcl-1 gene translocation was detected by PCR in 48% (10/21) of MCLs while no rearrangements were detected by PCR in case control DNA. Screening exons 5-8 of the p53 gene for mutations did not identify a single mutation in any of the MCL cases. No correlation was found between p53 mutations, the presence of a bcl-1 translocation, and the proliferative activity of neoplastic MCL cells. We conclude that these markers may demonstrate independent events which occur during the pathogenesis of MCL.