The importance of a high lambing percentage in early lambing flocks is well recognised as is the variability of the dose response to PMSG of early lambing ewes. It was hoped that the integration of the immunogen ovandrotone-albumin (Fecundin ® Coopers Animal Health) into such a system would give a reliable increase in ovulation rate without the danger of superovulation caused by higher doses of PMSG. Unfortunately, last year Logue, Gill and McClelland (1986) and Keeling, King and Gunn (1986) independently reported that although Fecundin treatment in early lambing flocks (using progestagen sponges with and without PMSG)gave an increased litter size over controls there was a considerable reduction infertility which negated this advantage. These groups employed a regime of a sensitising injection, a boosting injection 28-30 days later, and ram introduction to an induced oestrus after a further 28 days(i.e. a Boost Tupping Interval (BTI) of 28 days) for the second group and 35 days for the first.