Tritium labeled β-sitosterol was administered orally to 5 normal humans and to 5 terminal patients. Isolation of tritium-labeled sterols from plasma and red blood cells of normal male subjects showed some absorption had occurred, but it was much less than for comparable doses of labeled cholesterol. The highest level observed after a single 50-mg. dose of β-sitosterol was about 0.015 mg. per 100 ml. of blood in the total sterol fraction. These values are uncorrected for dilution by any unlabeled β-sitosterol present in the diet and are therefore minimum values. The disappearance rate from blood was slightly higher than for labeled cholesterol. Larger doses of tritium labeled β-sitosterol administered to a series of terminal patients gave similar results for blood levels and disappearance rates. Isolation of sterols from a variety of tissues showed β-sitosterol to be widely distributed. High specific activity values were observed in bile sterols, suggesting that β-sitosterol is selectively excreted by this route. Aorta and other blood vessels had lower amounts of tritium labeled sterols than most other tissues. The total amount of β-sitosterol present in blood and principal visceral organs (excluding intestine) was estimated in one patient as about 0.5 per cent of a single dose of 258 mg. given 5 days previously. Although the distribution pattern of absorbed β-sitosterol was similar to that of fed labeled cholesterol, it did not become esterified to as great an extent.