An autopsy case of I-cell disease was examined by histological, histochemical, ultrastructural and biochemical methods. Cultured fibroblasts contained numerous PAS- and oil-red O positive granules consistent with lysosomes. The beta-galactosidase activity was specifically low in liver of the patient. The fiboblast-like cells including the cardiac valves, periosteum and stromal cells of the organs were closely similar to those found in mucopolysaccharidoses histochemically as well as ultrastructurally. Lipid-like materials were observed massively in the myocardium and in the neurons of spinal ganglia, and from these organs excessive amount of ceramide tri-hexosides (CTH) was extracted. In a few hepatocytes the dense membrane-bound bodies suggestive of lipids were found by electron microscopy. Swollen glomerular epithelium contained strongly colloidal-iron positive material, but the amount of mucopolysaccharides in kidney was not elevated. In this paper, the relationship among the morphology, the material stored and the enzymes was discussed.