The effects of cooling rates and plunging temperature into liquid nitrogen (LN₂) on the survival of rapidly thawed bovine blastocysts derived from oocytes matured, fertilized in vitro and cultured in vitro or in rabbit oviduct were examined. The samples were cooled (0.3C/min for blastocysts developed in rabbit oviduct, 0.3 to 0.7C/min for blastocysts developed in vitro ) in 1.4M Glycerol from -5.2C to temperatures between -21 to -39C before transfer to LN₂. The highest levels of survival in vitro of blastocysts cooled at 0.3C/min were obtained after transfer to LN₂ from -24 to -39C in the blastocysts developed in rabbit oviduct. By contrast, the blastocysts developed in vitro survived as high as those developed in rabbit oviduct after plunging into LN₂ from -30C. The highest levels of survival and development in vitro of blastocysts developed in vitro were obtained after transfer to LN₂ from -30C (0.3C/min: 86% survival and 47% development) and from -33 to -36C (0.5C/min: 84 to 87% and 41%). The results indicate that blastocysts produced by in vitro system were more sensitive to cryoinjury than those developed in rabbit oviduct. The range of cooling rate and plunging temperature into LN₂ was limited when applied to blastocysts developedin vitro.