Telomeric sequences, located at the very end of the chromosomes, compensate for the chromosomal shortening as it happens after each round of cell division. Telomeric sequences influence the progress of cellular senescence and cancer progression. It has been reported that telomeres are shortened in acute leukemias where the cell turnover is high. B-cell chronic lymphocytic leukemia (CLL) is a particularly interesting haematological malignancy in regard to telomere dynamics because most of the malignant cells in CLL are mitotically inactive. In this study, we analysed the telomere length in patients with B-cell CLL in a comparison with the control group by using ddPRINS technique. Twenty patients with CLL and four healthy donors as a control group were included. We found short telomeres and no detectable telomeric repeats at the sites of chromosome fusion. We hypothesise that the telomeric erosion in CLL may reflect the dominance of malignant cells with an abnormally long life span. These cells may have encountered many antigenic stimulants in the past and hence underwent multiple clonal expansions. Our findings imply that shortened telomeres in CLL may be reflecting the "history" of the disease and serve as an independent prognostic factor. (c) 2004 Published by Elsevier SAS.