To develop the practical production of monozygotic twins in cattle, the ability of day 6 to 7 cow embryos to survive after they were split into two halves was tested. Day 6 to 7 embryos were recovered by the cervical method from superovulated Charolais heifers. Only normal embryos were selected at the advanced compaction stage when the cavity appears. Each embryo was cut into two halves and each half was replaced in an empty zona pellucida. After micromanipulation, the half embryos were directly transferred to recipient heifers via the cervix. From 16 normal embryos manipulated, 14 monozygotic half embryo pairs were obtained which were all transferred to 14 recipients (pregnancy rate 64.2 per cent); six recipients carried twins (twinning rate 66.6 per cent). Thus 15 fetuses were recorded from the 14 monozygotic half embryo pairs transferred.