The plasminogen and plasmin system, which is mainly regulated by urokinase-type plasminogen activator (uPA), its receptor (uPAR) and its inhibitor (PAI-1), is generally believed to play a role in cancer invasion and metastasis. This study was conducted to investigate the role of uPA, uPAR and PAI-1 in the invasion and metastasis of gastric adenocarcinoma. The expression of mRNAs for uPA and PAI-1 was determined by Northern blot analysis in nine primary gastric cancer tissues, nine paired metastatic lymph nodes and normal gastric mucosa. The mRNA of uPA was not or faintly detected in normal mucosa, while the expression was increased in both primary gastric cancer tissues and metastatic lymph nodes to a similar degree. The mRNA expression for PAI-1 in the gastric cancer tissues was not different from that in the paired metastatic lymph nodes and normal mucosae. uPAR was determined by immunohistochemical staining, demonstrating that five (56%) and six (67%) out of nine primary gastric cancer tissues and nine paired metastatic lymph nodes were positive, respectively and the intensity was stronger in metastatic lymph nodes. The results support the concept that most gastric cancer cells may have an innately moderate level of uPA and uPAR, and that increase of uPAR expression can be considered to be closely associated with cancer invasion and metastasis.