The development of efficient means of delivery genes in vivo is essential both for resting gene function in the intact animal and for human gene therapy procedures. A number of viral and non-viral gene delivery methods have been developed for this purpose. OF those herpes simplex virus (HSV)-based vectors have particular advantages for gene delivery to the nervous system including their ability to infect nondividing neurones and establish asymptomatic latent infections. Moreover, considerable progress has been made, firstly, in disabling HSV vectors so ns to prevent thr damaging effects of wild type virus and secondly, to ensure long-term expression of the inserted transgene(s). These vectors thus offer a valuable tool for testing gene function in neuronal cells in vivo and may ultimately be safe enough for use in human gene therapy procedures. (C) 2001 Elsevier Science B.V. All rights reserved.