SummaryThree different experiments were conducted in which horse embryos were frozen in liquid nitrogen, thawed and transferred surgically to synchronised recipient mares in two countries. In Experiment 1, out of 14 embryos transferred via mid ventral laparotomy, two established normal pregnancies, of which one continued to full term with the birth of a healthy colt foal. In Experiment 2, one of two embryos resulted in a normal conceptus. In Experiment 3, all the transfers were carried out via flank laparotomy and none of the recipients became pregnant. The results from Experiments 1 and 2 indicate that early unexpanded equine blastocysts tolerate cryopreservation better than larger expanded blastocysts. Some other factors associated with the transfer technique, unrelated to the viability of the frozen thawed embryos, are thought to have played a significant role in the failure to achieve any pregnancies in Experiment 3.