Seventy eight “barren” (ewes which were not pregnant prior to treatment) or early post-partum Karakul ewes were used. The interval from progestagen sponge withdrawal to oestrus was shorter within than outside of the breeding season and in both seasons increasing levels of PMSG caused a highly significant linear decrease in this interval. The oestrus response after synchronization was 100% within and not less than 88% without the breeding season with PMSG having no apparent effect. However, PMSG had a tendency to decrease the range of time during which ewes in a group commenced oestrus. The percentage of ewes which lambed was satisfactory when ewes were “barren” prior to synchronization. It was, however, low when synchronization commenced 20 days post-partum, the reason probably being that uterine involution was not complete and it is suggested that it should not commence before at least 28 days post-partum. PMSG increased the number of multiple births both within and without the breeding season. For a maximum twinning rate it is suggested that 250 l.U. PMSG within and 500 I.U. PMSG without the breeding season should be administered 30 hours before sponge withdrawal. Intra-uterine treatments with oestrogen or cortisol in post partum ewes had no effect on any of the above observations.