Subapical osteotomies were performed in the left quadrant of the mandibles and maxillas of five dogs and six monkeys. Two indirect methods, the isotope fractionation (diffusible tracer) and particle distribution (nondiffusible tracer--15mu microspheres) were used to quantitate local blood flow. To examine the effect of the surgery, blood flows in the alveolar bone, mucosa, and dental pulp of the segmented left quadrant and the corresponding tissues in the right quadrant were calculated and compared. It was assumed that the blood flows to the nonoperated right quadrant could serve as the controls to those observed in the osteotomized segment. The fractional decrease in blood flows to tissues in the operated sides were similar in both experimental animals. The decrease was largest in the dental pulp, ranging from 54% to 82% on the average, and least for the mucosal tissue, ranging from 18% to 40%. Blood flows decreased by 48% to 74%, on the average, in the alveolar bone. In some animals, blood flow to mucosal tissue that served as the pedicle was actually greater than the blood flow in the corresponding tissue on the right side. After surgery, the cardiac output in the dogs averaged about 156 ml/min/kg as calculated from both the diffusible and nondiffusible data. In the monkeys in which only the microspheres were injected, the cardiac output averaged 99 ml/min/kg. The arterial blood pressure dropped 8 to 13 mm Hg on the average (dog, 108 to 100 mm Hg; monkeys, 94 to 81 mm Hg). The heart rate also decreased slightly in dogs, 158 to 139 beats/min on the average; however, it increased slightly after the surgery in the monkeys, 144 to 161 beats/min. Blood losses during surgery were replaced wtih lactated Ringer's solution and the transient decreases in blood pressure of about 20 to 35 mm Hg were not sufficient to produce any shut down of renal blood flow.