One of the major limiting factors in practical exploitation of embryo transfer is the lack of a predictable and reliable supply of embryos on a regular basis. Superovulation requires the stimulation of significantly increased numbers of pre-ovulatory follicles by the administration of gonadotrophins mimicking the effect of follicle stimulating hormone (FSH). Ewes can be effectively superovulated using gonadotrophins given towards the end of a 12 to 14-day progestagen treatment, initiated without reference to the stage of the oestrous cycle (Boland et al., 1983). However, as in cattle (Goulding et al., 1991) there is a large variation in the follicular and ovulatory response in sheep. Although crude horse pituitary extracts will induce superovulation effectively in sheep, the lack of availability means that they are rarely used. The LH content in commercial FSH preparations has been indicated as contributing to some of the variation in the yield of transferable embryos in cattle following superovulation (Murphy et al., 1984). Recent preliminary data from this laboratory indicates that pFSH with a high LH:FSH ratio will induce superovulation in cattle and sheep. However, pFSH is normally given in multiple injections over 3 to 4 days which makes administration difficult. Therefore, an experiment was designed to assess the efficacy of a pFSH preparation with a high LH:FSH ratio to induce superovulation in sheep when given in either 4 or 6 injections. A second experiment compared the use of an ovine and porcine FSH preparation during superovulation in ewes.