1. Nasopharyngeal carrier states of several weeks to several months duration were induced in the Macaca mulatta by the intranasal inoculation with matt strains of group A streptococci.
2. Following such a successful inoculation with a particular type of group A streptococcus, the animal was usually resistant to reimplantation with that same type for several months to a year or more, although reimplantation with a heterologous type could generally be easily effected.
3. This resistance was shown to be closely correlated with the antibodies directed toward the type-specific M antigen, not toward the T antigen of the strains employed.
4. A majority (83.8 per cent) of the animals in which intranasal inoculation was followed by successful implantation developed significant increases in the antistreptolysin O titres of their sera; and in a limited number of instances, type-specific agglutinins and bacteriostatic antibodies were demonstrable in the animals' sera following successful implantation.
5. Nasopharyngeal carrier states could not be induced with the glossy, avirulent variants of group A streptococci; these animals, moreover, failed to show antibody responses and were susceptible to implantation with the matt variants of the homologous glossy strains.
6. The findings are in accord with the known facts regarding immunity to group A streptococci gained through experiments on rodents; and the possible relationship of these observations to the problem of type-specific immunity in human beings is discussed.