We investigated telomere length changes in patients with non-Hodgkin's lymphoma (NHL) receiving conventional-dose chemotherapy. Using Southern blot analysis, telomere length was measured in peripheral blood mononuclear cells from five NHL patients at diagnosis, 15 NHL patients after chemotherapy, and 39 healthy controls. Compared with age-matched putative normal controls, telomeres were significantly shorter in NHL patients at diagnosis. Mean telomere length was shorter after chemotherapy than before chemotherapy and was shorter after chemotherapy than in age-matched putative healthy controls. There was no correlation between the extent of telomere shortening and time elapsed after chemotherapy. These findings suggest that in NHL patients hematopoietic stem cells lose telomere length during the recovery period from bone marrow suppression after conventional-dose chemotherapy.