Transplantation of neural precursor cells (NPCs) is a potential tool to replace dysfunctional or degenerated neuronal or glial cell types in the central nervous system. Furthermore, transplantation of genetically engineered neural precursor cells might provide a strategy to target therapeutic gene products to the diseased nervous system. Here, we describe a novel and highly efficient electroporation-based transfection protocol for mitogen-expanded mouse NPCs. Transfection of NPCs with the reporter gene enhanced green fluorescent protein (EGFP) or the neural adhesion molecule L1 revealed transfection efficacies of more than 70% as estimated by the number of EGFP-positive or L1-immunoreactive cells 1 day after transfection in vitro. The percentage of EGFP- or L1-positive cells decreased with increasing time in culture. Positive cells were detectable for up to 3 weeks after transfection. When EGFP- or L1-transfected NPCs were grafted into the retina of adult wild-type or L1-deficient mice, they differentiated into glial cells some of which expressed EGFP and L1 for up to 2 and 3 weeks, respectively, the longest post-transplantation periods investigated.