Ultrastructural examinations of skin and/or rectal biopsy specimens were performed in 45 cases of various lysosomal storage diseases, including Pompe's disease, mucopolysaccharidoses I-IV, GM1 & GM2 gangliosidoses, Niemann-Pick disease, Gaucher's disease, metachromatic leukodystrophy, Fabry's disease, sialidosis, I-cell disease, mucolipidosis III, mannosidosis, fucosidosis, and ceroidlipofuscinosis. We found characteristic storage inclusions in all disorders except for Gaucher's disease, probably indicating the absence of storage outside the reticuloendothelial system. In some cases of adult-onset neurolipidosis and ceroid-lipofuscinosis, the examination of the rectal submucous plexus neurons was important to detect characteristic inclusions, suggesting some superiority of the rectal biopsy to the skin biopsy in these conditions. On the contrary, because of the absence of the myelinated fibers in the rectal mucosa, the skin biopsy seems to be superior to the rectal one in diseases affecting the myelin sheath primarily. These morphological studies about skin and/or rectal biopsy specimens are useful to support the diagnosis obtained by the biochemical methods, to be a clue to diagnosis of cases in which biochemical defects of the disease are still unclear, and to make a probable diagnosis of some lysosomal storage diseases in atypical cases showing neurodegeneration.