The immunohistochemical expression of tenascin was examined in the normal adult mucosa of the stomach, primary tumours and lymph node metastases of gastric cancer patients. In normal gastric tissue tenascin was expressed in the muscularis mucosae, muscularis propria and vessel walls, however it was not expressed in either the mucosal connective tissue or the stromal tissue in the submucosal layer. In gastric cancer, tenascin was expressed in 35 of 85 primary tumours, and in 8 of 25 metastases in lymph nodes. Tenascin was located in the fibrous stroma surrounding foci of cancer. The expression of tenascin in the primary tumour did not correlate with the depth of invasion, lymph node metastasis or prognosis. Tenascin appears during the process of either malignant transformation or tumour progression in gastric cancer, and the positive expression of tenascin may be useful as a stromal marker for the early detection of gastric cancer.