Pex13 encodes an SH3-containing peroxisomal membrane protein required for the import of proteins into peroxisomes. In humans, mutations in PEX13 can disrupt peroxisome biogenesis and lead to peroxisomal metabolic dysfunction and neurodegenerative disease. We report here on the mouse gene Pex13 and its encoded protein. Mouse Pex13 spans 18 kb and consists of four exons. We detected Pex13 transcripts in all mouse tissues tested, with highest levels in liver and testis. The Pex13 open reading frame predicts a 44.5-kDa protein that displays 91% sequence identity to the human PEX13 protein. We have localized PEX13 protein to peroxisomes in mouse liver and show that this protein also sorts to peroxisomes in human skin fibroblasts. These data indicate that the structure and properties of the mouse and human PEX13 proteins are almost identical. We infer from these findings that targeted disruption of mouse Pex13 would provide an appropriate model for the study of PEX13 dysfunction in humans.