Until recently, methods to detect abnormalities in fat absorption have been based on procedures that are difficult to obtain and technically difficult to perform in the average hospital, i. e. fecal fat studies, chylomicron counts, vitamin A tolerance tests, and plasma lipid determinations. A measure of pancreatic enzymes by intubation techniques is likewise not generally available. The accessability of I131-labeled triolein now makes it possible to study fat absorption much more readily. Since Thannhauser and Stanley first reported their results, in 1949,1 a large experience has accumulated which attests to the simplicity and reliability of the method. We have attempted to evaluate the radioactive fat (RAF) test in a large general hospital, where, because of laboratory limitations, the assessment of fat malabsorption has always been difficult. The present study reviews our findings with 200 such tests. Procedure In general, we have followed the procedure outlined by Ruffin.