A human primary gastric cancer tissue (adenocarcinoma II-III) was transplanted into nude mice (SWISS/DF. nu/nu). It has been transferred for 8 generations at 56 sites in 28 nude mice with transplantable rate of 100%. The transplanted tumor is designated as transplantable human primary gastric cancer-1 in nude mice (THPGC-1). The growth of THPGC-1 is rather rapid and the size of transplanted tumor reaches 1 cm2, 4-5 weeks after transfer. The morphology and histochemistry of the original tumor were retained well in the initial and serial transplanted tumors. THPGC-1 could secret carcinoembryonic antigen (CEA). After intravenous or intraperitoneal injection of 131I-antiCEA monoclonal antibody into the THPGC-1 bearing nude mice, the radiolabeled antibody was concentrated and localized in the tumor as shown by gamma-camera analysis. Similar pattern of lactate dehydrogenase isoenzyme was observed both in primary gastric cancer tissue and THPGC-1 tissue. Chromosomal examination revealed that THPGC-1 was human aneuploid ones. Southern blot analysis showed that the pattern of repetitive DNA bands and the structures of 28s, rDNA, c-H-ras and c-myc genes in THPGC-1 were identical to the original primary gastric cancer DNA. The results suggest that THPGC-1 be a reliable model for the research of the molecular biology of cancer cells and experimental gastric cancer diagnosis and treatment.