The relative levels of cyclin D1 (CCND1) (a) and (b) transcripts were determined by real-time reverse transcription polymerase chain reaction (RT-PCR) and found to vary according to the tissue origin in both control and tumor samples. A five-fold overexpression of both isoforms was observed in 28/38 cases of mantle cell lymphoma (MCL) and of only one isoform in 10/38 MCL. No correlation was observed between expression of cyclin D1 isoforms and CCND1 genotype at position 870.