Telomerase, a ribonucleoprotein, stabilizing chromosomes by adding telomeric repeats to their ends, is highly expressed in most neoplastic cells and has a critical role in cellular immortalization. In this study, telomerase activity was measured in the peripheral blood mononuclear cells of patients with non-Hodgkin lymphoma (NHL). A total of 18 patients with B-cell NHL and 12 healthy volunteers were included in the study. Of the patients 7 (38.9%) were found to have telomerase activity, but no activity was detected in control subjects. No correlation was found between the telomerase activity and the grade of the disease. When the patients were divided into two subgroups as follicular and non-follicular NHL, telomerase activity was detected in 5 of 10 follicular NHL (50%) and 2 of 8 non-follicular NHL (25%) samples, but these results were not found statistically significant. In conclusion, there is detectable telomerase activity in peripheral blood of some patients with NHL, possibly suggesting the existence of neoplastic cells in the circulation or activation of lymphocytes.