The peroxisomal disorders can be divided into three classes: firstly, those in which the activity of only one single enzyme is reduced; secondly, those in which the activities of multiple peroxisomal enzymes are deficient and also the number of peroxisomes is reduced; and thirdly, those in which the activities of multiple peroxisomal enzymes are lacking and at the same time the number of peroxisomes is normal at least in liver tissue. The cerebro-hepato-renal syndrome of Zellweger is the prototype of peroxisomal disorders of the second group. Clinical distinction between Zellweger syndrome and neonatal adrenoleukodystrophy or infantile Refsum disease can be impossible. The clinical abnormalities that should give rise to suspicion for the presence of a peroxisomal disorder and urge the necessity of further biochemical studies are proposed.