1. Monkeys convalescent from a paralytic attack of poliomyelitis develop humoral antibodies slowly; in the present series their first appearance in most was at 2 months and in some not until 3 months after the attack.
2. Convalescent monkeys display resistance to reinfection with the same strain by the nasal route long before antibodies become demonstrable in their serum, in this respect differing from many vaccinated monkeys whose serum neutralizes the virus, while they remain susceptible to nasal infection.
3. When antibodies appear in the serum of resistant convalescent monkeys, they are not quantitatively greater than in the serum of vaccinated monkeys which succumb to infection. As regards resistance to infection, humoral antibodies, therefore, do not have the same significance in vaccinated as in convalescent poliomyelitis monkeys.