Thymidine phosphorylase (dThdPase) is identical to platelet-derived endothelial cell growth factor (PD-ECGF), an angiogenesis factor. We investigated the correlation between dThdPase activity in gastric cancer tissue and clinicopathological factors. Thirty-three cancer tissue specimens and 23 adjacent normal gastric mucosal specimens were obtained from surgery. Measurement of dThdPase activity was based on the amount of 5-fluorouracil formed from 5'-deoxy-5-fluorouridine by dThdPase. Mean dThdPase activity in cancer tissue was approximately 3.2 times higher than that in normal tissue. Cancerous tissues with venous invasion had about twice the dThdPase activity as cancerous tissues without venous invasion. Other clinicopathological features were not related to dThdPase activity. A correlation between dThdPase activity and immunosuppressive acidic protein level was observed (r = 0.532, P = 0.005). dThdPase activity in gastric cancer cells was found to be correlated with venous invasion, supporting previous findings that it plays a role in tumor angiogenesis.