A total of 155 follicular oocytes were recovered from 20 pregnant mare’s serum gonadotrophin–human chorionic gonadotrophin (PMSG–HCG)-treated heifers 24–30 h after the HCG injection. The oocytes were classified as stimulated if surrounded by an expanded cumulus and unstimulated if surrounded by a compact cumulus. Sixty stimulated and 25 unstimulated oocytes were transferred into bovine oviducts and 30 stimulated and 40 unstimulated oocytes were transferred into pig oviducts inseminated surgically with bovine semen. The oocytes were recovered by slaughtering the recipients 16–24 h after transfer. None of the 8 unstimulated oocytes recovered from the bovine tracts and none of the 18 unstimulated oocytes recovered from the porcine tracts were fertilized. However, 5 of the 22 stimulated oocytes and 6 of the 9 stimulated oocytes recovered from bovine and porcine tracts, respectively, were found to be fertilized as evidenced by pronuclear formation and the presence of sperm components within the cytoplasm.