Abstract Electron micrographs of Cryptococcus laurentii cells reveal glycogen granules throughout the cytoplasm. Glycogen phosphorylase (α-1,4-glucan: orthophosphate glucosyltransferase, EC 2.4.1.1) is bound to these granules and has been obtained in purified form upon isolation of homogeneous preparations of these granules. The enzyme has a pH optimum close to 6; its K m values are: 1.5 mM for P i , 0.65 mg/ml for glycogen, and 1 mM for Glc-1- P . The K m for Glc-1- P is substantially lower, 0.4 mM, in the presence of Mg 2+ , whereas v max remains unchanged. The enzyme is not activated by AMP. Glc-6- P , glucose nucleotides, AMP, ADP, and ATP are inhibitors of the enzyme. Mg 2+ reverses the inhibition by nucleotides and sugar nucleotides. A Glc-6- P -dependent glycogen synthetase is also bound to the glycogen granules of this organism.