We evaluated a spectrophotometric nitroblue tetrazolium (NBT) reduction assay as a technique to quantitate experimental intestinal ischemic injury. NBT is a tetrazolium salt that is reduced by mitochondrial coenzymes to form a blue formazan dye which can be measured on a spectrophotometer. We used a rat model of progressive intestinal ischemia to compare NBT reduction with standard histologic grading by light microscopy. Isolated segments of small intestine were made ischemic for periods of 15, 30, 60, 90, and 120 min in each of five rats (no reperfusion). A portion of each segment was prepared for both NBT reduction assay and blinded histologic grading. The reproducibility of these results was then tested in a second identical study of four rats (Part 2). When compared to nonischemic segments of intestine, NBT reduction was significantly decreased after 30 min of ischemia (P < 0.05, ANOVA) and continued to decrease as ischemic time increased. These findings were reproduced in the second experimental group. Overall, NBT reduction correlated closely with duration of ischemia (r = 0.81, P < 0.001) and histologic grade (r = 0.77, P < 0.001). Based on criteria developed in Part 1, NBT reduction had a sensitivity of 100% and a specificity of 94% for detecting ischemia > or = 30 min in Part 2. We conclude that the spectrophotometric NBT assay in an accurate technique for quantitating small intestinal ischemic injury which also gives useful information about the functional status of mitochondria.(ABSTRACT TRUNCATED AT 250 WORDS)