Abstract 1. 1. A study has been made of the histochemically demonstrable glycogen of rat liver particulate fractions obtained by differential centrifugation of sucrose homogenates. 2. 2. Histochemically demonstrable glycogen was found in mitochondria, microsomes, a poorly sedimentable fraction of proteinaceous material isolated by centrifugation at 13,000 g, and as particulate glycogen not associated with proteinaceous material. No glycogen could be demonstrated histochemically in isolated nuclei. 3. 3. Quantitative chemical determinations of glycogen on these fractions were in general agreement with the histochemical findings. 4. 4. In terms of ratio of glycogen to nitrogen contents of the particulate fractions, microsomes were highest, and mitochondria lowest. 5. 5. The use of calcium ion to agglutinate mitochondria resulted in the carrying down of a markedly increased fraction of the total nitrogen of the homogenate, without any increase in the fraction of total glycogen in these particulates. 6. 6. Despite the carrying out of all operations in the cold room, a very large fraction of the total glycogen initially present in the liver was found as reducing sugar. 7. 7. The occurrence in liver of particulate glycogen not associated with protein, first reported by Lazarow, is confirmed. 8. 8. An appreciable fraction of the total glycogen content of liver is present in solution in the cytoplasm.