Docosahexaenoic acid (DHA), a major component of membrane phospholipids in brain and retina, is profoundly reduced in patients with peroxisome biogenesis disorders (Zellweger syndrome). Supplementing newborn patients with DHA resulted in improved muscular tone and visual functions. The purpose of this study was to investigate (a) whether DHA levels were also reduced in newborn PEX5 knockout mice, the mouse model of Zellweger syndrome that we recently generated; (b) whether these levels could be normalized by supplying DHA; and (c) whether this results in longer survival. The DHA concentration in brain of newborn PEX5-/- mice was reduced by 40% as compared with levels in normal littermates; in liver, no differences were noticed. The daily administration of 10 mg of DHA-ethyl ester (EE) to pregnant heterozygous mothers during the last 8 days of gestation resulted in a normalization of brain DHA levels in Zellweger pups. However, no clinical improvement was observed in these pups, and the neuronal migration defect was unaltered. These data suggest that the accretion of DHA in the brain at the end of embryonic development is not only supported by the maternal supply but also depends on synthesis in the fetal brain. Furthermore, the DHA deficit does not seem to be a major pathogenic factor in the newborn Zellweger mice.