Electron microscopic studies were performed on the rectal mucosa from patients with mucopolysac-charidoses, mucolipidoses and sphingolipidoses. The following results were obtained. 1) Ultrastructural studies of the rectal mucosa obtained by biopsy using intestinal biopsy capsule were found to be useful in the diagnosis of lysosomal storage disease. 2) Between each pathological state a characteristic difference in intracellular accumulative deposits was seen in its distribution, volume and morphology. 3) Unlike mucolipidoses and sphingolipidoses, the intracellular accumulative deposits could not be seen in the endothelial cells in mucopolysaccharidoses. 4) Although an identical enzyme (a-L-iduronidase) is believed to be the underlying enzymatic defectof Hurle\u27s syndrome, Hurler-Scheie compound and Scheie\u27s syndrome, the intracellular accumulativedeposits in Schwann cells were found in Hurler\u27s syndrome, but could not be seen in Hurler-Scheiecompound and Scheie\u27s syndrome. 5) In Morquio\u27s syndrome, the intracellular accumulative deposits were limited to histiocytes unlikeother mucopolysaccharidoses. 6) In Gsu-gangliosidosis type 2, the intracellular accumulative deposits showed characteristic struc-tures. These were limited to histiocytes unlike other mucolipidoses. 7) In a new type of mucolipidosis,described by Horino et al., the characteristic intracellularaccumulative deposits different from those in other mucolipidoses were seen in the histiocytes and Schwann cells. 8) Intracellular accumulative deposits in sphingolipidoses were characteristic each entity. In Tay-Sachs disease, the intracellular accumulative deposits were observed in Schwann cells and axons. In Gaucher\u27s disease, no Gaucher cells or intracellular accumulative deposits could be seen in the lamina propria. In Niemann-Pick disease (acute neuronopathic form, type A), intracellular accumulative deposits were observed in the majority of cells of the lamina propria, but in Niemann-Pick disease (chronic nonneuro-nopathic form, type B), no intracellular accumulative deposits could be seen in Schwann cells and axons. 9) It is suggested that the presence and volume of intracellular accumulative deposits in Schwann cells and axons correlate to the degree of the mental retardation in the studied cases. 10) In the comparative studies of the various stages of the disease, an increase of intracellular accumulative deposits in histiocytes and Schwann cells occured in Hurler\u27s syndrome; the number of histiocytes containing intracellular accumulative deposits increased in Gm-gangliosidosis type 1, and increases in the type of cells containing intracellular accumulative deposits occured in Mucolipidosis II, in advanced stages. These changes could not be seen in Niemann-Pick disease (chronic nonneuronopathicform, type B)
