The increasing incidence of human exocrine pancreatic cancer has created a need for an adequate animal model for human disease. The objective of this study is to determine whether DSL-6 transplantable acinar cell tumor will undergo phenotype shifts when grown in culture and then transplanted back into rats. The basic goal is to regraft the tumor and see what the phenotype is after a period in culture. A transplantable tumor as DSL-6 was derived from a primary acinar cell carcinoma of the pancreas. The carcinoma developed in a male Lewis rat that was given 3 intraperitoneal 30 mg/Kg injections of azaserine (a diazoketone carcinogen) when the rat was 3 weeks of age. Histologically, the tumor was a moderately well differentiated acinar cell carcinoma with a microcystic phenotype. Serial subcutaneous transplants have grown as moderately to poorly differentiated acinar cell carcinomas. These transplants served as the source of cells for culture. After 4-6 weeks, cultured tumor cells were inoculated subcutaneously into young male Lewis rats. Tumors from rats were collected and examined by light microscopy and electron microscopy. The rat model has been quite useful to understand tumor histogenesis, even though the pancreatic neoplasms they develop do not resemble those that constitute the most common type encountered in humans, namely ductal adenocarcinomas.