A disorder has been described with clinical, chemical, and pathological features remarkably similar to those of the Zellweger’s cerebrohepatorenal syndrome. However, in the Zellweger syndrome, peroxisomes cannot be detected in hepatocytes and renal tubular epithelium, using cytochemistry or ultrastructural examination, whereas in the pseudo-Zellweger syndrome, hepatocytes contain abundant peroxisomes, many of which are larger than normal. Study of peroxisomal enzyme activities reveals that the dihydroxyacetone phosphate acyltransferase activity is not diminished, while the activity of this enzyme is severely reduced in the Zellweger syndrome. Dihydroxyacetone phosphate acyltransferase is an enzyme bound to the peroxisomal membrane, and its presence in the pseudo-Zellweger syndrome is consistent with the morphological observation of abundant peroxisomes. The biochemical abnormalities consist of an accumulation of very long-chain fatty acids, pipecolic acid, and abnormal bile acids. There is good evidence that the basic defect involves the peroxisomal enzyme 2-oxoacyl-CoA thiolase, an enzyme of the ß-oxidation chain. Thiolase is probably involved not only in the oxidation of very long-chain fatty acids but also in the biosynthesis of bile acids.