The action patterns of liver and muscle glycogen synthetases and of muscle phosphorylase b on glycogen samples of different molecular weight and on ,&amylase limit dextrins were studied. For this purpose a method for measuring the number of newly added glucose residues that are a t non-reducing ends was developed.It was found that glucose transfer to the non-reducing ends of glycogen catalyzed by liver glycogen synthetase and muscle phosphorylase followed a Poisson distribution.The number of outer chains in the glycogen molecules available to both enzymes appeared to be smaller than the actual number of outer chains in the polysaccharide. The number of such available chains diminished as the glycogen was heavier. For the same glycogen sample, the number of available chains to phosphorylase appeared to be equal or smaller than that to glycogen synthetase.