Mesenteric infarction and other acute ischaemic intestinal diseases are still a challenging diagnostic problem. Based on animal experiments, intestinal fatty acid binding protein (I-FABP), which is uniquely localised to the bowel, has recently been proposed as a new serum marker for intestinal ischaemia. This paper reports on two cases with acute intestinal ischaemic diseases, and the measurement of serum I-FABP by western blot analysis. The concentrations of ordinary serum markers were normal and the bowel necrosis was not diagnosed until surgical exploration. Immunochemical analysis showed that the I-FABP concentrations in the patients' serum samples were high at the time of admission, and that I-FABP was undetectable in the samples obtained after bowel resection and in healthy control subjects. This paper suggests that I-FABP is released into the circulation in the acute phase of intestinal ischaemia and that I-FABP can be used in establishing the diagnosis of ischaemic intestinal diseases.