The biochemical analysis of a case of infantile neuronal ceroid lipofuscinosis, as determined by clinical and neuropathological findings, is presented. A diminished amount of solids is found, the amount of lipids is 30% of the normal as expressed in lyophilized tissue. The yield of myelin isolated by the density gradient is 1.8% of the normal. Phospholipid patterns show a reduction in ethanolamine phosphoglyceride, N-acetylneuraminic acid is extremely low and sphingolipids are largely reduced, cerebrosides being most affected (2.5% of the normal). In cerebrosides and sulfatides the decrease in very long chain fatty acids is important, but the deficiency in any type (including hydroxy compounds) is not too dramatic. According to the aspect under electron microscopy, the density profile, and the biochemical composition of the subfractions, isolated myelin is close to normal. The loss of the myelin sheath appears to reflect a Wallerian degeneration in the CNS: myelin loss is a secondary effect. This disease, from a biochemical point of view, seems to be the ideal control for leukodystrophies.