The use of viral vectors for gene delivery to motor neurons in vivo has been hampered by the need to perform invasive surgery to inject directly the vector into the anterior horn of the spinal cord. Here, we have characterized the features of herpes simplex virus-1 (HSV)-derived vectors, in terms of gene mutations and promoter constructs, that are required to allow efficient transduction of motor neurons following a relatively noninvasive peripheral administration via sciatic nerve or footpad injection. Owing to the wide variety of animal models used to study neurodegenerative diseases of motor neurons, we analysed the effectiveness of these vectors in adult mice and adult and neonatal rats. We tested viruses with differing degrees of disablement based on the 1764 backbone (deleted for ICP34.5 and an insertional inactivation in VP16) rendered completely replication incompetent by the deletion of the essential immediate-early genes ICP27 and/or ICP4. In the adult mouse, prolonged gene expression in motor neurons was obtained after sciatic nerve inoculation with a vector defective in ICP4 and ICP27. In the adult rat, both the vector defective in ICP4 and the vector defective in ICP4 and ICP27 were capable of transducing motor neurons for extended periods of time during viral latency. This study demonstrates the feasibility of using HSV vectors for persistent transgene expression in motor neurons in a safe and nontoxic manner following peripheral administration. These vectors are potentially useful tools to investigate the functions of genes involved in motor neuronal survival and regeneration in models of motor neuron diseases in vivo.