Peroxisomes were the latest subcellular organelles to be discovered. For a long time, due to limited knowledge of their function, peroxisomes were considered to play only a supporting role for other organelles in cellular metabolism. The discovery of specific metabolic pathways carried out exclusively in peroxisomes and, in particular, the description of genetically determined peroxisomal disorders such as the Zellweger syndrome and X-linked adrenoleukodystrophy, established the importance of these organelles in playing an essential role in cellular metabolism. Recently, their participation in the metabolism of reactive oxygen species and free radicals was found to be one of the important functions of peroxisomes. The fact that peroxisomal disorders are well defined biochemically and that peroxisomes consume a significant amount of the total cellular oxygen uptake, make cells from patients suffering from these disorders a suitable cell model for studying peroxisomal participation in the detoxification of reactive oxygen species.