Abstract
Beginning at the first or second day of life, dosages of 500 µg. of testosterone propionate per 100 gm. body weight were administered daily to intact and castrated guinea pigs. There was no statistically significant evidence that the intromission and ejaculation responses developed precociously in these animals, when compared with intact guinea pigs receiving sesame oil. These results differ from those obtained with the rat in which precocious sexual development has been produced by testosterone propionate treatment. It was concluded from the accumulated evidence that the guinea pig and rat do not respond similarly to testosterone propionate during post-natal development and maturity.