Adm. of testosterone propionate for periods varying from 20-90 days to immature [female] rats and adults in diestrus at time of the first inj. resulted in small ovaries containing follicles, mucified vaginae, large uteri and a hyperplastic en-dometrium. The mammary glands presented an increase of fibrous tissue and duct development. In adults first treated in the same way during estrus the ovaries were larger and contained hypertrophied corpora lutea; mucification of the vaginae was intensified; the uteri were enlarged; and the breasts showed proliferation of acini as well as ducts. The use of chorionic gonadotrophin following a long course of testosterone resulted in a rapid enlargement of the ovaries with the formation of corpora lutea.