Five cases have been presented with evidence of disordered glycogen metabolism. Two cases of glycogen storage disease of the liver are included which were confirmed by biopsy, together with clinical and laboratory evidence. Treatment of one of the cases with adrenocorticotropic hormone resulted in a disappearance of hypoglycemia and acetonuria during the period of therapy. Two cases of glycogen storage disease of the heart are reported together with clinical histories and necropsy reports. An ECG which was recorded on one of the patients is included. A case of galactosemia is reported together with extensive laboratory evidence of marked galactose intolerance. The criteria for the diagnosis of these entities are reviewed and the symptomatology, physical findings, treatment, prognosis and pathologic manifestations are discussed.