In the central nervous system, oligodendrocytes synthesize vast amounts of myelin, a multilamellar membrane wrapped around axons that dramatically enhances nerve transmission. A complex apparatus appears to coordinate trafficking of proteins and lipids during myelin synthesis, but the molecular interactions involved are not well understood. We demonstrate that oligodendrocytes express several key molecules necessary for the targeting of transport vesicles to areas of rapid membrane growth, including the exocyst components Sec8 and Sec6 and the multidomain scaffolding proteins CASK and Mint1. Sec8 overexpression significantly promotes oligodendrocyte morphological differentiation and myelin-like membrane formation in vitro; conversely, siRNA-mediated interference with Sec8 expression inhibits this process, and anti-Sec8 antibody induces a reduction in oligodendrocyte areas. In addition, Sec8 colocalizes, coimmunoprecipitates and cofractionates with the major myelin protein OSP/Claudin11 and with CASK in oligodendrocytes. These results suggest that Sec8 plays a central role in oligodendrocyte membrane formation by regulating the recruitment of vesicles that transport myelin proteins such as OSP/Claudin11 to sites of membrane growth.