We reported earlier an 8-1/2 year old boy with a constellation of findings(progressive developmental delay, micronodular cirrhosis, elevated very long chain fatty acids in plasma and skin fibroblasts) consistent with both neonatal adrenoleukodystrophy (nALD) and Zellweger syndrome (ZS). This patient's peroxisomal status was re-evaluated when he reached 20 years of age as his clinical course was inconsistent with either nALD or ZS. We now report the presence of acyl-CoA oxidase (an enzyme with peroxisomal targeting signal-1 motif) and 3-ketoacyl-CoA thiolase (an enzyme with peroxisomal targeting signal-2 motif) in this patient's catalase negative peroxisomes. This suggests that both PTS-1 and PTS-2 mediated protein transport processes into peroxisomes are normal in this patient. Catalase, which is imported into peroxisomes by a pathway different from PTS-1 and PTS-2, is present in the cytoplasm rather than in the peroxisomes in this patient. The inhibition of catalase with aminotriazole in control decreases peroxisomal functions in fatty acid (lignoceric acid and phytanic acid) oxidation and synthesis of plasmalogens to levels similar to the partial activities observed in cultured skin fibroblasts from the index patient. This suggests that the partial peroxisomal activities in this patient may be due to inactivation of peroxisomal enzymes by excessive hydrogen peroxide present in catalase-deficient peroxisomes. It may be possible that in this patient the abnormality in catalase translocation into peroxisomes may be due to a defect in the pathway which includes topogenic signal in catalase and/or receptor and import machinery in the peroxisomal membrane. These findings of catalase negative peroxisomes of normal density and normal PTS-1 and PTS-2 import machinery with partial peroxisomal functions clearly differentiates this patient from those with known disorders of peroxisomal biogenesis.