Investigations were made on the spread of fixed rabies virus after its inoculation into the rear foot-pads of rats. The presence of rabies virus in the central nervous system was first detected in the lumbar segment of the spinal cord. Removal of the sciatic nerve or of its fasciculus, either before or soon after challenge, drastically lowered mortality, thus giving evidence of a rapid neural spread of the infection. Neither the perineural structures nor the axons appeared to be involved. Although the presence of virus in the sciatic nerves was first demonstrated by the development of neutralizing antibodies in the serum of rats "immunized" by multiple injections of nerve material from rats killed 48 hours after challenge, resection of nerves had to be carried out long before that time to be effective in preventing viral progression.