In order to assess the role of telomerase in development of malignant gastric cancer, we measured the telomerase activity in gastric cancer tissues and normal tissues obtained from 95 patients by employing recently developed sensitive PCR (polymerase chain reaction)-based telomerase assay (telomeric repeat amplification protocol, TRAP). We also investigated how telomerase activity related to other clinicopathological findings including DNA ploidy and K-RAS gene point mutation. The telomerase activity was present in 85 of the 95 gastric cancer tissues, whereas we detected no telomerase activity in any normal tissue. The incidence of telomerase activity in gastric cancer tissues was not correlated to age, sex, tumour stage, histological grade, DNA ploidy or K-RAS mutation. Disease-free or overall survival of patients having tumours with detectable telomerase activity was not significantly different from that of those without telomerase activity. These findings suggest that telomerase may play a key role in the establishment and progression of the gastric cancer and further studies will be needed to elucidate the biological role of telomerase in gastric cancer.