The expressions of epidermal growth factor (EGF) and its receptor were studied immunohistochemically in a total of 156 gastric carcinomas; 26 early and 130 advanced. No EGF immunoreactivity was found in early carcinomas, while EGF-positive tumor cells were detected in 38 (29.2%) of the 130 advanced carcinomas. EGF receptor immunoreactivity was detected in one (3.8%) of the 26 early carcinomas and in 44 (33.8%) of the 130 advanced carcinomas, the incidence being significantly different (p less than 0.01). Out of the 130 advanced carcinomas, 17 (13.1%) had synchronous expression of EGF and its receptor and most of the tumors with strong expression of EGF were positive to EGF receptor. A significant correlation was observed between the depth of tumor invasion and EGF or its receptor immunoreactivity in tumor cells (p less than 0.05). Furthermore, a good correlation was demonstrated between the synchronous expression of EGF and its receptor and the depth of tumor invasion or the tumor staging. The incidence of cases with EGF in metastatic tumors was significantly higher than that in primary tumors (p less than 0.05). Patients with synchronous expression of EGF and its receptor had a far poorer prognosis than those without EGF and receptor.