Intracerebral infection of weanling Swiss mice with a temperature-sensitive (ts) mutant of vesicular stomatitis virus (VSV), ts pi364, resulted in a unique neuropathological syndrome not previously described with other VSV mutants. Mice infected with wild-type VSV died from an acute encephalitis characterized by neuronal necrosis and efficient virus replication in both brain and spinal cord. In contrast, with VSV ts pi364, the most prominent histopathological feature was destruction of the ependyma of the lateral ventricles. Virus antigen was also limited to the leptomeninges and the lateral ventricles. Infected mice survived and developed hydrocephalus. Replication of ts pi364 in the brain was 10- to 100- fold less than that of wild-type VSV, and appearance of virus in the spinal cord was delayed. VSV ts pi364 was isolated from mouse cells persistently infected with VSV. Another VSV ts pi mutant, isolated from the same persistent infection, behaved in vivo like wild-type VSV, even though both mutants were very similar in plaque size, reversion frequency, cut-off temperature, and synthesis of virus-specific proteins at semipermissive temperature. These results strongly suggest that VSV ts pi364 has a second, non-ts mutation which results in a restricted target cell range in vivo; wild-type VSV can infect both neurons and ependymal cells, whereas ts pi364 does not replicate in neurons.