X-linked adrenoleukodystrophy (ALD) is a degenerative neurological disease characterized by the accumulation of very long chain fatty acids in various tissues and demyelination of the central nervous system. The human gene responsible for the disease encodes a membrane-bound ATP-binding transporter protein that is located in peroxisomes. We isolated the mouse adrenoleukodystrophy gene, determined its structure, and mapped it both cytogenetically and genetically. The mouse gene is very similar in structure to the human gene, consisting of 10 exons arranged over a 22-kb genomic region. We localized it in band B of the mouse X chromosome by fluorescence in situ hybridization analysis and, using a new microsatellite repeat polymorphism, determined the map location as 47 cM from the X centromere. We found evidence for other sequences in the mouse genome related to the 3' end of Aldgh. This study paves the way for the construction of gene-targeting plasmids that may be used to develop an animal model of ALD.