We analyzed immunohistochemically the association between p53 tissue status and prognostic parameters of 357 gastric cancer patients, using endoscopically obtained biopsy materials, embedded in paraffin. Using PAb1801, an anti-p53 monoclonal antibody p53 immunoreactivity was detected in the nuclei of cancer cells in 113 cases (32%). The nuclear p53 immunoreaction was closely associated with positive lymph node metastasis, serosal invasion, and liver metastasis. For the estimation of proliferative activity, proliferating cell nuclear antigen (PCNA) labeling rates (LRs) of biopsy specimens were immunohistochemically measured. A significant positive correlation was found between PCNA LRs and p53 tissue status. In addition, a positive nuclear p53 immunoreaction was found to be significantly associated with shorter overall survival. Especially, in the group of patients with stages III and IV, the prognosis of patients with p53-positive tumours was significantly poorer than that of patients with p53-negative tumours. These results indicate that immunohistochemical staining for nuclear p53 in biopsied materials may be useful in deciding the therapeutic schedule of patients with gastric cancer, preoperatively.