We studied fixation of bromodeoxyuridine by immunohistochemistry in 17 patients with advanced gastric cancer. Macroscopically, they corresponded to Borman's types III (n = 10), IV (5) I (1) and unclassified (1). 11 patients had a diffuse lesion, 5 an intestinal type lesion and 1 an epidermoid carcinoma. Positive reactions were observed in 27.7% of cells (95% CL 10-48%). No difference was observed in positivity of superficial (29%) or deep areas of the tumor (27%). Greater fixation rates were observed in patients under 50 years, of age compared to older patients. The percentage of positive reactive cells was not related to macroscopic or histologic tumor type. Greater fixation rates were observed in this series compared to those previously reported, suggesting greater proliferation rates in these patients.