The birth of young from frozen-thawed mouse embryos transferred to recipient females and frozen mouse embryos transported successfully from North America to the United Kingdom has been reported. Of the domestic species, continued development in vivo and in vitro was achieved with cattle and goat embryos stored in liquid N2. Cattle embryos were collected at Christchurch, New Zealand, from mature parous cows of mixed dairy breeds 7-8 days after AI[artificial insemination] with semen from a Simmental bull. All embryos were morulae or early blastocysts and after collection they were frozen in Dulbecco''s phosphate buffer enriched with 25% bovine blood serum (DB+S) and containing 1.5 M dimethylsulfoxide (DMSO) or 1.0 M glycerol. The embryos in freezing tubes were then cooled to -50.degree. C at rates of 0.13 or 0.3.degree. C/min and crystallization was initiated at -3.degree. C by the addition of crystals of frozen DB+S. The embryos were then transported in liquid N2 containers by air to Sydney, Australia, and then by road (120 km) to Mittagong. After storage in liquid N2 for 2-3 mo. the embryos were thawed as described by Bilton and Moore. The tubes were then warmed to 30.degree. C (0.7.degree. C/min) and the DMSO and glycerol were removed by dilution. Embryos (10 of 24) developed in culture to expanded blastocysts, the remaining 14 showing little or no development. The 10 developed embryos and 6 of those which showed little or no development were transferred to the uterine horns of 11 recipient cows which were in estrus 7 1/2 - 8 1/2 days earlier. Uterine palpation per rectum at 8 and 12 wk and 5 mo. after transfer indicated that 5 of the 11 recipients were each carrying a single fetus and they subsequently gave birth to 5 live and apparently normal calves. All 5 had received 1 embryo which had developed in culture. Frozen cattle embryos can be transported over considerable distances without marked loss of viability.