The concentration of pristanic acid was measured in plasma from a patient with an isolated peroxisomal very long chain fatty acid (VLCFA) acyl-CoA oxidase deficiency, a defect in peroxisomal beta-oxidation resulting in accumulation of VLCFA in plasma and tissues. Although peroxisomes are believed to be involved in pristanic acid beta-oxidation, the pristanic acid level in the patient's plasma was within the control range. This finding provides evidence for the existence of a pristanyl-CoA oxidase distinct from the specific trihydroxycholestanoyl-CoA and VLCFA acyl-CoA oxidases.