Hormonal factors are known to influence parturition and the condition of the young. Interference with parturition in the rat has been reported with pituitary and placental extracts and pregnancy urine pituitary implants,,1e luteal extracts, hypophysectomy, estrogens, and androgens. The present report deals with some of the permanent effects on female rats whose mothers received andro-genic substances during pregnancy. Study has been made of 10 female young which have grown to maturity and have either been sacrificed or have died from abnormalities resulting from effects of androgen injections in their mothers. Female young, born after adequate androgenic treatment of the pregnant mother (500 gamma of testosterone propionate in 0.1 cc. of peanut oil injected subcutaneously daily during the last third of pregnancy), superficially resemble males in that the clitoris is large and penis-like, the perineum extensive and. scrotum-like, and the pin-point vaginal opening absent. (1) Upon gross inspection no vaginal aperture was seen (Fig. 1) and the peripheral portion of the vagina was absent beyond a small tubercle about 1 cm. from the perineum. The fluid-containing cavity within the uterus and cervical portion of the vagina was abruptly terminated at the tubercle. (2) The nipples were either absent or were markedly underdeveloped. Absence and underdevelopment were seen in the same animal. Mammary glands were nearly normal in appearance. (3) The internal reproductive system with the above exceptions was intact and some degree of ovarian function was evidenced by uterine, vaginal, and mammary histology, by the presence of follicles and corpora lutea, and by fluid in the uterus and vagina. (4) The uterus and existent portion of the vagina were greatly bloated with retained fluid in 6 of the animals (Fig. 1). The dimensions of the expanded uterine cervix and vagina were as great as 35×30×32 mm. Apparently this large distension by fluid, which followed the assumption of functional activity of the reproductive system, proved fatal in the majority of these animals, seemingly partly by compression of the colon. The urinary system was also affected, the bladder and urethra being held taut by the subjacent expansion of the reproductive system. The preliminary study of permanent abnormalities in rats resulting from injections of hormones to the mother during pregnancy, suggest the following inferences: (a) Pseudohermaphroditism may be produced by androgen injection, the females presenting a masculine appearance with a penis-like clitoris, scrotum-like perineum and an absence of proper development of the nipples and the outer portion of the vagina. (b) The absence of nipples in the normal male rat may be correlated with the presence of male hormone. (c) Possible harmful effects on the foetus must be guarded against in clinical use of hormonal substances in large amounts or at critical times during pregnancy.