Blastocysts, obtained from cows on Day 10-11 after oestrus, were cultured for 20 h. Most (81.3%) blastocysts grew in culture and about 50% took up glucose. There was no morphological difference between the blastocysts which did or did not take up glucose but development in vivo was better for blastocysts which had taken up glucose (69.2%) than for those which did not (14.2%).