Adult albino rats of both sexes were fasted 48 hrs. and given 1.5 ml. of corn oil (1.385 [plus or minus] 0.01 g.) by stomach tube under light ether anesthesia. After fully recovering consciousness (1-2 min.) the rats were subjected to the following partial pressures of O3: 117, 80, 63, and 53 mm. Hg (corresponding approx. to altitudes of 8,000, 18,000, 24,000 and 28,000 ft., respectively). Simultaneously fed controls were kept at atmospheric pressure. Four hrs. after feeding the amt. of fat absorbed was detd. by measuring the amt. of fat remaining in the alimentary tract. At partial pressures of O2 of 117 and 80 mm. Hg, the amt. of fat absorbed was not significantly different from that in the control animals, but at partial pressures of O2 of 63 and 53 mm. Hg the amt. absorbed was significantly less; statistically, the difference was highly significant. Apparently the threshold for the absorption of fat in the rat lies between partial pressures of O2 of 80 and 63 mm. Hg. Eanges of anoxia compatible with life evidently do not interfere, as far as fat absorption is concerned, with proper nutrition.