We have extended our recent observation that human gastric cancer cells (MKN-45) synthesize and secrete an hEGF-like immunoreactive factor (designated as EGF-LI) by characterization of EGF-LI produced by five human gastric cancer cell lines in culture. Two cell lines (MKN-45 and KATO-III) derived from poorly differentiated adenocarcinoma synthesized and secreted a much larger amount of EGF-LI than three cell lines (MKN-1, MKN-28, and MKN-74) derived from well-differentiated adenocarcinoma. Treatment of MKN-45 cells by retinoic acid reduced significantly synthesis and secretion of EGF-LI, suggesting that production of EGF-LI is dependent on differentiational state of gastric cancer cells.