beta-[14C]Sitosterol was evaluated for its usefulness as a nonabsorbable marker of lipid absorption in intubation studies. A liquid meal, including [3H]triolein as a marker of absorbable lipid, was used. The beta-sitosterol was shown to remain well mixed with triolein in the gastric antrum, validating its suitability for this type of study. In small bowel fluid, the beta-sitosterol was shown to partition into the aqueous phase in proportion to triolein and its hydrolysis products. With this system, lipid absorption was shown to take place chiefly in the jejunum in normal individuals.