The aim of this study was to evaluate the vitrification efficiency of in vitro produced bovine embryos, by following both in vitro survival and pregnancy rates after thawing.Embryos were obtained using a complete in vitro procedure, with development in co-culture, as previously described by Ectors et al. (Livestock Production Science, 36, 29-34, 1993). At day 7 after fertilization, grade 1 and 2 embryos were divided into three groups: morulae and early blastocysts (M), normal blastocysts (B) and expanded blastocysts (EB).The vitrification procedure was performed in two steps, according to Mahmoudzadeh (PhD, Ghent, Belgium, 1994). Briefly, embryos were equilibrated in VS1 (20 % v/v ethylene glycol in PBS + 0.4 % BSA) for 3 minutes and then rinced in VS2 (40 % v/v ethylene glycol, 18 % w/v Ficoll and 0.3 M sucrose in PBS + 0.4 % BSA) and placed in a 0.25 ml straw containing the VS2. After a total of 45-60 sec exposure to VS2, straws were plunged into liquid nitrogen. Straws were thawed in a 40°C water bath for 5-10 seconds, and the contents of the straw expelled into a Petri dish containing 3.5 ml PBS + 0.4 % BSA. Most thawed embryos were co-cultured and survival and hatching was determined after, respectively, 48 and 72 h of culture. Some thawed and untreated (control) blastocysts were stained with Hoechts 33342 and the number of cell nuclei was counted. Finally, a total of 40 thawed EB were transferred into 20 synchronized heifers (2 embryos/recipient).In conclusion, this vitrification procedure appears to be an efficient alternative for cryopreservation of in vitro produced bovine embryos.