Attempts were made to induce pregnancy in androgen-sterilized rats. Because it is known that the preovulatory LH surge is absent in androgen-sterilized rats, a classical approach was taken to circumvent the probable deficit in cyclic release of LH by giving a subcutaneous injection of LH-RH (400 ng) every four days. Cyclic injection of LH-RH induced a regular estrus cycle in the greater part of treated females, whereas a saline-treated control group showed a persistent estrous smear. The number of eggs recovered and the mating rate increased with subsequent treatment with LH-RH, indicating a priming effect by the initial injection. However, when mated animals were autopsied on day 10 (sperm = day 1), no pregnancies had occurred. When a pituitary gland was transplanted from a normal rat into the kidney capsule of an androgen-sterilized rat in order to maintain functional corpora lutea, implantation occurred in 38% of the group of females treated with five separate LH-RH injections. Endometrial trauma in androgen-sterilized rats elicited a better response in the group which received multiple LH-RH injections than the group which received a single injection. These results indicate that the cyclic LH surge may be a necessary factor for induction of pregnancy in androgen-sterilized rats.