Unfertilized eggs recovered from donor rabbits shortly after ovulation induced by injection of HCG, were transferred to the oviducts of recipients at 9–10.25 h after insemination with 200 million spermatozoa and injection with HCG. At this same time, the recipient’s ovaries were covered with nail polish to prevent the entry of her own eggs into the oviducts. Placing a ligature at the ampullar-isthmic junction of one oviduct of the recipient immediately before the transfer of eggs, reduced the percentage of eggs penetrated during 1.5 h to 14 from 48 in the oviduct similarly ligated at the utero-tubal junction. Delaying the ligation of the ampullar-isthmic junction until 0.25 h after egg transfer did not increase sperm penetration, which was 17% in the ligated compared to 38% in the contralateral nonligated oviduct. However, delaying the ligation until 0.5 h after egg transfer permitted normal sperm penetration, 49% being penetrated in the ligated versus 46% in the nonligated oviduct. Since a delay of this magnitude should have permitted only 21–29% of eggs to be penetrated, if sperm movement in the oviduct was random, this result was taken as indirect evidence of a stimulation by the products of ovulation of sperm movement from the proximal isthmus to the site of fertilization. Additional experiments were performed to obtain direct evidence to support this supposition. Various substances were placed in one oviduct of recipients at 9.75–10.5 h after insemination and injection with HCG, and 0.5 h before ligation of the oviduct at the ampullar-isthmic junction and transfer of rabbit eggs to both oviducts. Frozen rat eggs in cumulus, or frozen rabbit eggs in cumulus, or 50 µl of Ringer’s solution did not enhance penetration. However, after transfer of freshly ovulated rat eggs in cumulus 29 and 36% of eggs were penetrated in the ligated and nonligated oviducts, respectively. These figures did not differ significantly. Fresh rabbit cumulus with eggs removed or rabbit eggs with adherent corona cells following removal of the cumulus with hyaluronidase had no stimulating effect. Thus the experiment with fresh rat eggs provided further evidence for a stimulatory effect of the products of ovulation on sperm transport in the oviduct. The failure of rabbit cumulus or rabbit eggs without cumulus to produce a similar effect leaves open the question of which component of the products of ovulation produces this stimulatory effect.