Ultrastructural study of 2 human renal adenocarcinomas demonstrated abundant myelinoid lamellated cytoplasmic inclusions, which were restricted to the neoplastic cells. They were structurally similar to those reported in renal adenocarcinomas chemically induced in rats; to those described in human diseases involving defects in lipid metabolism, including Gm2 gangliosidosis, Fabry's disease, Nieman-Pick disease, and juvenile-type neuronal ceroid-lipofuscinosis. Similar inclusions have also been reported to be induced by several drugs, none of which were taken by these patients. The occurrence of these lamellated inclusions in 2 human renal adenocarcinomas reinforces the phenotypic similarity between nitrosomorpholine-induced renal adenocarcinomas in rats and some renal adenocarcinomas seen in humans.