Abstract
A single adm. of 5 mg. estradiol benzoate in the 1st part of the menstrual cycle in baboons caused massive atresia of the graafian follicles. Multiple injs. caused disappearance of almost all large and small graafian follicles. A single inj. of 5-20 mg. of progesterone on the 8th to 10th day of the cycle was followed by rapid de-turgescence of the perineum. The ovaries developed one and at most 2 large follicular cysts in which the cumulus oophorus could be identified. There was an atresia of some larger follicles. Combinations of estradiol benzoate and progesterone given in the early cycle caused massive atresia as well as cystic ovaries. Such treatment was associated, in 3 of 4 baboons, with abnormal bleeding while the perineum was in a state of almost maximal turgescence. Estradiol benzoate given in the early cycle was a useful technic for inducing follicular atresia, whereas progesterone consistently induced cysts on the ovaries. A new clue is afforded to the understanding of the etiology of cystic ovaries in the human [female].