In 2 trials, 346 porcine in vivo blastocysts were vitrified in heat-softened and pulled French straws by the Open Pulled Straw (OPS) vitrification method. After thawing, embryos were either cultured in vitro (n=89) for 24 to 48 hours or transferred surgically (n=257) to 11 synchronised recipients without further culture. In trial I. 88% and 71 % of thawed blastocysts reexpanded and hatched in vitro, respectively, while 71 % reexpanded in trial 2. However, no piglets were born following transfer. though 1 recipient was diagnosed pregnant at Day 56 of gestation.