Recent studies have suggested the possible involvement of the kallikrein-kinin cascade in gastric inflammatory diseases and malignant transformation in peptic ulcers. Germ-line mutations of genes responsible for repairing DNA mismatch may cause the transformation of chronic peptic ulceration to malignancy. The aim of the study was to compare the expression of the serine protease, tissue kallikrein (TK) and kinin peptide receptors, B1 and B2, in human gastric carcinoma and ulcers. Furthermore, experiments were designed to ask the question whether holistic changes known to occur in carcinoma would be reflected in the expression of the neutrophil kallikrein-kinin cascade. Expression of tissue kallikrein and kinin receptors in both tumour and ulcer tissue and circulating neutrophils of cancer and ulcer patients was determined by immunolabelling techniques, using specific antibodies. The immunolabelled images were visualised by light, confocal and electron microscopy. This is a first study that provides strong evidence for enhanced expression of TK in peptic ulceration and gastric malignancy, suggestive of a crucial role for serine proteases in cancer.