Infantile female rats were subcutaneously injected with 2.5 mg testosterone within two days. The majority of the rats responded to this treatment with opening of the vagina, and about 50% developed an estrus. However, corpora lutea were not formed. Equally treated animals received additionally 0.2 i.u. HCG -- a dose which is inffective when given alone -- distributed on the second and third day of experiment. After this treatment an increased number of rats reacted with estrus and the development of corpora lutea. In infantile female rats, follicles stimulated by testosterone were also transformed into corpora lutea by an injection of 0.025 mg clomiphene citrate.