Radiolabeled N-(2-aminoethyl)-glycine (AEG) was synthesized and various aspects of its bioavailability were evaluated. AEG was rapidly and completely taken up by the small intestine of the rat. It was quickly absorbed into the portal vein. Most of the absorption took place during the first hour, with a peak at 30 min. Entry of this compound into the intestinal mucosal cell may be by a mechanism not involving active transport. Of many organs examined, only the liver took up significant amounts of AEG. The latter neither crossed the brain barrier nor was metabolized. Total urinary excretion (as intact AEG) averaged 80% of the administered dose within 4 hours and nearly 100% by 10 hours. Excluding the neutral-acidic amino acids and ammonia, AEG represented >99% of the ninhydrin positivity in the urine. AEG is thus an example of a substance which is rapidly and totally absorbed, as well as quickly and completely excreted.