Rabbit blastocysts were cultured in vitro at 37CC for 8, 16 or 24 hr in modified Flo medium. Subsequent transfer to suitable recipient does revealed that blastocyst viability was maintained in vitro for at least 16 hr. The percentage of viable foetuses developing from blastocysts cultured for at least 8 hr was equal to that from noncultured blastoctsts.