Charcot-Marie-Tooth disease (CMT) is the most common inherited neuropathy in humans and has been associated with a partial duplication of chromosome 17 (CMT type1A). We have generated a transgenic rat model of this disease by overexpression of the peripheral myelin protein 22 (PMP22, gas-3) gene. We have used this animal model to investigate the biochemical composition of purified myelin membranes. We can show that PMP22 is increased in abundnance in purified myelin of transgenic animals. This suggests that the stoichiometry of myelin proteins may be altered in CMT1A. In addition, nano ESI-MS/MS was employed to determine quantitative differences in the lipid composition between wildtype and CMT rat myelin. Here, the total cholesterol and phospholipids appeared 50% reduced in CMT rat (in relation to myelin proteins), wheras the relation between cholesterol and phopholipids was unchanged. Differences were also observed between the fatty acid composition of galactoceramide (GalC) with an increase of the hydroxylated long fatty acids (FA 24:0-OH) in transgenics. Taken together, our data suggest that the abnormal stoichiometry of myelin proteins and lipids may contribute to myelin instability in the rat model of CMT, and possibly to the secondary axonal loss which is responsible for the clinical phenotype in human CMT1A.