Rapid plasma reagin (RPR) titers were periodically examined during and after treatment in three rabbits clinically diagnosed with rabbit syphilis. RPR titers remained positive after clinical recovery and then gradually declined. Of the two rabbits inoculated experimentally, one showed clinical signs of the disease, while the other did not. RPR titers were also periodically evaluated before and after inoculation in these two rabbits. The trends in RPR titers reflected the course of infection, both in the spontaneous and in the experimental cases. An inapparent case and cases without clinical signs after clinical recovery showed low titers for long period of time. Useful information for interpretation of RPR titers measured clinically was obtained by this survey.