Peroxisomes are single membrane bound organelles present in virtually all human cells (Gould et ai 2001). Their morphology is typically spherical, and their abundance per cell varies with the metabolic state. The peroxisome membrane contains a unique set of peroxisomal membrane proteins. The peroxisome matrix is a dense protein rich environment and contains about 70 enzymes involved in numerous metabolic processes including 6-oxidation of straight and branched chain very long and long chain fatty acids, synthesis of cholesterol and ether-lipids, and oxidation of D-amino acids and polyamines. Peroxisomal proteins are encoded by nuclear genes and synthesized in the cytosol on free ribosomes. Newly synthesized proteins contain specific peroxisomal targeting signals that direct them to and into the peroxisomes. For the matrix proteins, these include a C-terminal targeting signal PTS1 and an N-terminal signal PTS2. The targeting signals for membrane proteins are still poorly understood. The importance of peroxisomes is underlined by the existence of an expanding group of monogenetic disorders in which there is impairment of peroxisome biogenesis and functions.KeywordsComplementation GroupTruncation MutationZellweger SyndromePeroxisome BiogenesisChondrodysplasia PunctataThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.