Three tests of small intestinal function were performed at 3100 m and 4846 m to seek evidence of malabsorption of high altitude. Xylose tolerance did not change in 11 subjects but, in three who ascended to 5600 m, one-hour xylose levels were significantly lower. The results of an oxalate loading test did not suggest significant fat malabsorption. A direct fat absorption test using chylomicron levels after ingestion of 100 g fat showed significantly increased levels at high altitude. We conclude that there is no evidence of malabsorption up to 4846 m.