In an attempt to elucidate various histological features of gastric cancers, seven human gastric adenocarcinomas were studied in vitro and in nude mice. Growth pattern of each cultured cell line in vitro corresponded well to the histological type of parent tumor. The cell lines, MKN7, MKN74, and MKN28 derived from differentiated carcinomas showed morphological characteristics of intestinal differentiation in cell polarity and microvilli with core-filaments in vitro as well as in nude mice. However, they gradually diminished the characteristics in course of time. The cell lines, MKN 45 and OKAJIMA, derived from undifferentiated carcinomas, had natures of not only ordinary gastric mucosa but also intestinal metaplastic mucosa. They seem to have multipotentiality for differentiation, and preserved well the natures for long periods of culture. The KWS-I cell line composed of undifferentiated cells in vitro displayed the potential for differentiation in nude mice. However, the differentiation of KATO-III cells derived from a signet-ring cell carcinoma was suppressed in nude mice. The common abnormality of chromosome was not found, and the growth rate in vitro was not dependent on the histological type of parent tumor.