An orthotopic xenograft of the human pancreatic tumor was established by inoculating human pancreatic tumor AsPC-1 cells into the duodenal lobe of the pancreas of the athymic nude mouse. Microscopically, the xenograft was formed by a heterogeneous population of tumor cells, displaying moderately to poorly differentiated adenocarcinomas with the latter capable of invading the adjacent pancreatic islets or non-endocrine elements. At 4 weeks post-transplantation, the tumor was detectable as a focal implant at the site of inoculation and thereafter grew progressively leading to extensive visceral invasion and metastasis. In contrast to the subcutaneous xenograft, all the mice (9/9) bearing orthotopically transplanted tumor developed secondary foci in the gut and at the peritoneum, with 7, 6, and 4 animals showing additional kidney, mesenteric lymphnodal, and diaphragm metastases, respectively. Distant metastases in the lungs were found in 3 mice and malignant ascites developed in two. Human pancreas cancer associated antigen was detected in the tumor, serum, and ascitic fluid of the mice at 63 +/- 24 micrograms/gm, 15 +/- 6 micrograms/ml, and 5 micrograms/ml, respectively. The finding of these regional and distant metastases was quite different from that in the animal bearing subcutaneously xenografted tumor where no metastases to internal organs was observed. The results suggest the potential use of this experimental system in tumor biology and antigen expression of human pancreatic cancer in vivo.