The derivation of specialized differentiated cells from embryonic stem (ES) cells is now a major focus for future therapies involving cell and organ replacement in humans. To obtain populations of differentiated cells for transplantation into the human body, highly optimized protocols are needed that allow direction of the development of ES cells and their derivatives. These protocols mostly include the use of a combination of growth factors that control the differentiation of ES cells into highly specialized cells found in adult organs. The introduction of different growth factors into ES cells and their derivatives via viral gene transfer may greatly facilitate the optimization of these protocols. In this chapter, we describe a method based on herpes simplex virus type 1, which allows efficient gene transfer during several steps of a protocol, directed to obtain neural progenitors from ES cells. This protocol therefore may allow the study of potential factors influencing the cell fate or differentiation of ES cells and their derivatives.