Using in situ hybridization with a cloned DNA probe specific for the VSV G protein, viral RNA was detected and localized in CNS tissue of mice infected i.c. with either wild or ts G 31 VSV mutant. In both cases, brain and spinal cord neurons were the only cells seen to contain viral RNA. Virus-positive neurons were observed enclosed in spongious areas induced by the ts VSV mutant. These results suggest that the VSV shows a strong tropism for the neuronal cell and indicate that the vacuole formation might be associated with the expression of the VSV G protein gene in infected neurons.