To determine which heterotopic transplantation sites produce competent oocytes from vitrified ovarian cortical tissue. Randomized, longitudinal, in vivo. Ovarian cortical pieces (3x6x0.5 mm3) from adult (n=4; 6-9 yrs) and peripubertal (n=4; 4-5 yrs) rhesus macaques were vitrified using glycerol:ethylene glycol containing non-permeating polymers, placed into straws and cooled in LN2 with cryoprotectants removed in sucrose [1]. Within the same animal, pieces were transplanted to subcutaneous (sc) sites [2,3] in the arm (n=4); sc abdomen (n=4); sc abdomen + omental tissue (n=2) or retroperitoneal + omentum (n=2); and bilateral mesosalpinx sites (n=2). Serum was analyzed for estradiol (E) and progesterone (P) to determine ovarian cyclicity during one year post-transplantation. When E reached at least 100 pg/ml and the preovulatory follicle was 3-6 mm diameter, hCG (1000 IU, im) was given [3]. In alternate cycles, follicles were aspirated 30 hr later. Mature oocytes were inseminated in vitro. All animals resumed cyclic ovarian cyclicity based on midcycle E rise and luteal phase P. There was no difference in the time to the first cycle post-transplantation between adult (5.9±0.8 mos) and peripubertal (6.0±0.8) animals, or the number of ovarian cycles displayed during the year (7±1 vs 6±1, respectively). The total number of preovulatory follicles seen in the sc arm (2) and sc abdomen (2) was less (P<0.01) than those seen in the sc abdomen + omentum (14), retroperitoneal + omentum (10) and mesosalpinx (11). A single preovulatory follicle typically developed at a single site within each animal during a given month despite the presence of multiple transplants. The numbers of preovulatory follicles observed and oocytes collected were similar between adults and peripubertal animals. Of 38 total follicles that developed, 31 were aspirated yielding 21 oocytes (68%); 52% metaphase II, 24% metaphase I, 24% degenerated and no immature oocytes. Three oocytes fertilized, and two cleaved to the 4-cell (from mesosalpinx) and 8-cell stage (retroperitoneal + omentum), and one developed to a morula (sc abdomen + omentum). Vitrified ovarian cortical tissue transplanted to retroperitoneal or sc abdominal sites containing omentum and in the mesosalpinx consistently developed a single preovulatory follicle and produced steroid hormones typical of normal ovarian cycles. A competent oocyte was retrieved from each of these sites and efforts to produce offspring are ongoing. Heterotopic transplantation of vitrified ovarian tissue is promising for cancer survivors seeking fertility who sustain extensive ovarian damage after cancer therapy that may preclude re-vasculariztion to support orthotopic transplantation.