To investigate prognostic indicators for gastric adenocarcinomas in advanced stage, we have carried out immunohistochemical determination of thymidylate synthase (TS) in carcinoma tissues. Sixty seven cases of curatively resected gastric carcinoma, under 70 years old at the time of surgery, who had been in the same grade of invasion and lymph nodal involvements (pT3/pN2, Stage IIIB), and had underwent postoperative 5FU-related chemotherapy for a long period were extracted from the files of our hospital. Formalin-fixed and paraffin-embedded specimens were stained with an antibody for human TS (polyclonal). A positive signal was always compared with some types of inflammatory cells in the same slide because of their constantly strong signal. Normal control tissue used was human bone marrow containing blastic cells. Both staining intensity and the fraction of positively stained carcinoma cells were examined in each case, and then the results were summarized with respect to fraction of positively stained carcinoma cells. The present study indicates that the TS-negative group had better survival than the positive group (p < 0.05), the 5 year survival rates being 42.3% and 25.1%, respectively, which suggests that the frequency of TS-positive carcinoma cells could also be a prognostic indicator.