Intestinal ischaemia with ensuing gangrene has been a serious clinical problem. Delay in diagnosis has inevitably led to either massive gut resection or death. It has been shown that the bowel contains high concentrations of both organic and inorganic phosphate. With gut ischaemia, phosphate is released from the bowel and elevated concentrations may be measured in peripheral blood, peritoneal fluid and urine. Associated leucocytosis and acidosis constitute a diagnostic laboratory triad. The alteration in gut phosphate metabolism has been studied extensively in dogs and humans. Under hypoxic conditions, a time period exists before irretrievable gut necrosis ensues. During this vital interval serum phosphate is elevated. In 20 clinical cases an accurate diagnosis of bowel ischaemia was made utilizing phosphate measurements. Three cases had an early diagnosis which led to embolectomy with no loss of gut. Elevated serum phosphate is an accurate diagnostic finding in early cases of massive gut ischaemia. It is hoped that this simple test may help lower the staggering mortality and morbidity associated with massive intestinal ischaemia.