This protocol is an extension to:Nat. Protoc. 1, 1552-1558 (2006); doi:10.1038/nprot.2006.276; published online 9 November 2006This article describes how to reliably electroporate with DNA plasmids rodent neuronal progenitors of the hippocampus; the motor, prefrontal and visual cortices; and the cerebellum in utero. As a Protocol Extension article, this article describes an adaptation of an existing Protocol and offers additional applications. The earlier protocol describes how to electroporate mouse embryos using two standard forceps-type electrodes. In the present protocol, additional electroporation configurations are possible because of the addition of a third electrode alongside the two standard forceps-type electrodes. By adjusting the position and polarity of the three electrodes, the electric field can be directed with great accuracy to different neurogenic areas. Bilateral transfection of brain hemispheres can be achieved after a single electroporation episode. Approximately 75% of electroporated embryos survive to postnatal ages, and depending on the target area, 50-90% express the electroporated vector. The electroporation procedure takes 1 h 35 min. The protocol is suitable for the preparation of animals for various applications, including histochemistry, behavioral studies, electrophysiology and in vivo imaging.