Immunohistochemistry was applied to AMeX-fixed tissue sections of 12 adenocarcinomas of the stomach (seven intestinal adenocarcinomas and five diffuse carcinomas), 12 adenocarcinomas of the pancreas (nine ductal adenocarcinomas and three signet ring carcinomas), and 12 squamous cell carcinomas of the larynx obtained at surgical resection to examine the possibility of extravascular activation of blood coagulation in cancer tissues by exploring the in loco patterns of distribution of fibrinogen, a final product of blood coagulation, fibrin, and a by-product of coagulation reactions (prothrombin fragment 1+2). Gastric, pancreatic, and laryngeal cancers exhibited fibrinogen antigen in abundance throughout the tumor stroma. Fibrin was detected along the edges of nests of carcinoma cells and at the host-tumor interface. Prothrombin fragment 1+2 was present in the blood vessels in areas of neoangiogenesis at the host-tumor interface (gastric and pancreatic cancer tissues) and on the tumor cell bodies (pancreatic and laryngeal cancer tissues). The presence of prothrombin fragment 1+2 in cancer tissues appears to be a good indicator of coagulation activation and thrombin generation at the tumor burden.