1. Multiple paralytic doses of poliomyelitis virus (RMV strain), when brought together with small amounts of synthetic ascorbic acid in vitro, are rendered non-infectious as determined by intracerebral injection of such mixtures into rhesus monkeys. 2. Vitamin C administration to monkeys infected intranasally with the RMV strain produces results which differ in accordance with the technique employed for nasal instillation. With an infection of maximum severity, induced by flooding the nasal portal of entry with large amounts of virus, vitamin C administration fails to exert any demonstrable influence on the course of the disease. With a less forceful method of droplet instillation, the picture of the disease in control animals becomes so variable that the results cannot be easily interpreted; but the available data suggest that vitamin C treatment may be a factor in converting abortive attacks into an altogether non-paralytic infection. 3. The administration of synthetic vitamin C to monkeys infected intracerebrally with small doses of the RMV strain gives results comparable to those previously obtained with this substance in monkeys infected intracerebrally with the Aycock strain of poliomyelitis virus. 4. The implications of the findings are discussed.