In experimental small bowel obstruction an increased proportion of smooth endoplasmic reticulum and an increased number of lysosomes were seen in many liver cells. The occurrence of cytoplasmic vacuoles as well as the glycogen depletion were not pathognomonic and in the toxic pathogenesis the ultrastructural damage in the liver was only of a low degree and can be explained as a reactive (e.g. detoxication) phenomenon. The increase of plasma corticosterone content (stress reaction) differed only slightly from that of the controls, but a severe disturbance of fluid balance (increase of hematocrit and decrease of serum Na+ and C1-) and circulation failure were the more conspicuous findings, compared to toxic liver cell disturbance in the pathogenesis of small bowel obstruction.