The controlled in vivo testing of gonococcal antigens, which in the past has been limited by the absence of a suitable model in laboratory animals, is important to the development of an effective immunizing agent for gonorrhea. Experimental infections with Neisseria gonorrhoeae have been recently reported, however, in four species of laboratory animals: rabbits, guinea pigs, hamsters, and mice. When the infection in each of these species was considered and the potential use of the species as a laboratory model was evaluated, the guinea pig was found to be the most satisfactory species for study of the immune mechanism of gonococcal infections. Both active and serum-mediated passive immunity were demonstrated in the guinea pig model.