The hypermethylation of p16ink4a and p15ink4b genes have been described as an inactivating mechanism alternative to deletions and mutations that accounts for a relatively high proportion of cancers, including non-Hodgkin's lymphomas (NHLs). To investigate whether detection of abnormal methylation could have clinical applications in the management and follow-up of lymphomas, we have analysed the behaviour and evolution of p16ink4a and p15ink4b methylation in 13 NHL cases undergoing chemotherapy. All cases were also analysed for the presence of monoclonal rearrangements of immunoglobulin or T-cell receptor genes. Six patients showed methylation in at least one of these genes at diagnosis, whereas in two other cases methylation appeared during the treatment. The other five cases were always unmethylated. Methylation was detected when any histological or molecular evidence of disease was present, suggesting a good correlation between methylation and disease. In some cases, we were able to detect methylation in patients at complete remission and without evidence of monoclonal cell population, indicating a high sensitivity of the PCR to detect methylation. These results suggest that p16ink4a and p15ink4b methylation could be good markers of disease and could be helpful in identifying lymphoma patients at risk of relapse.