We have isolated several new genes that are specifically expressed by oligodendrocytes in the CNS. This was achieved by differential screening of a rat spinal cord cDNA library with probes derived from normal and from oligodendrocyte-free spinal cord mRNAs. Four of these genes are exclusively expressed by oligodendrocytes: Three of these are not related to known genes, whereas one encodes the myelin oligodendrocyte glycoprotein (MOG). Four other genes are expressed by oligodendrocytes as well as by Schwann cells. One gene codes for apolipoprotein D, which is thought to be involved in lipid metabolism. A second cDNA sequence codes for the recently identified galactosylceramide-synthesizing enzyme UDP-galactose:ceramide galactosyltransferase. The third gene encodes a small protein with four putative transmembrane domains that is related to a T-lymphocyte-specific membrane protein, MAL. The fourth gene encodes the rat homologue of the stearyl-CoA-desaturase 2 (SCD2) gene, which is specifically expressed in the nervous system and involved in the synthesis and regulation of long-chain unsaturated fatty acids essential for myelination. Finally, we found that a member of the beta-tubulin family is highly expressed in oligodendrocytes as well as neurons. The identification of several new proteins that may play a role in myelin synthesis and sheath formation will lead to new insight into this complex mechanism.