d-Glucose-1-C 14, -2-C 14, and -6-C 14 were fed to cuttings of buckwheat ( Fagopyrum tataricum Gaertn.) and 24–48 hr later the rutin was isolated and hydrolysed. This gave d-glucose, l-rhamnose and quercetin all with the same specific activity and suggests that all components of rutin came from the same carbohydrate metabolic pool. Both rhamnose and glucose were degraded by methods which allowed estimation of C 14 in each of the six carbon atoms. The rhamnose was apparently derived from glucose without rearrangement of the carbon skeleton. l-Rhamnose-1-C 14 and l-fucose-1-C 14, fed to buckwheat, were not incorporated into rutin.