Plasminogen activator inhibitor-1 (PAI-1) is inhibitor of plasminogen activator(PA) which is serine protease involving proteolytic degradation of the extracellular matrix and tumor invasion and metastasis. Detailed analysis of the PAI-1 in malignant tissues has not yet been reported. To investigate whether expression of PAI-1 in gaatric adenacarcinoma correlates with lymph node metastasis, immunohistochemical analysis using monoclonal antibody for this antigen was performed in 101 cases of gastric adenocarcinomas. Specific immunostaining was detected in the cytoplasm of the cancer cells and was not detected in stromal cells. Expression of PAI-I was evident in 61% of gastric adenocarcinomas with lymph nade metastasis and 38% without lymph node metastasis (p<0.05) But, the PAI-1 expressian is not related to the number of lymph node metastasis and histopathologic grade. The results support the suggestion that PAI-1 may play a crucial role in metastatic progression of gastric adenocarcinoma and may serve to modulate proteolysis by PA.