Adult male albino rabbits challenged intratesticularly with viable Spirochaete pallida suspension and kept at 3° C .or 21° C developed syphilomata at the same rates. Adverse environmental temperatures apparently do not enhance or decrease the rabbit's resistance to the challenge. Rectal temperature measurements during the experimental period show no gross differences in animals kept at 3° C or 21° C, and the temperatures remained quite constant throughout the experiment.