An attempt has been made to measure the capillary blood flows through the individual tissues of the ileum of normal dogs and those which were in endotoxin shock. The technic used was based upon the assumption that the uptake of D2O by the tissues was limited by the capillary flow. In loops from endotoxin shock dogs which were perfused at normal blood pressure (135 mm. Hg), the tissue perfusion ratios calculated on this assumption were reduced to about one-half of the control value in the mucosa and to about three-fourths in the submucosa and muscularis, despite the fact that total blood flow was unchanged. When the loops from shock dogs were perfused at the dog's pressure (70 mm. Hg), there was a further decrease of about 50 per cent in both the total blood flow and the tissue perfusion ratios. It is concluded that this reduction in tissue capillary flow, especially in the mucosa, may be the basis of the pathological changes in the intestine in endotoxin shock.