Twenty South African Mutton Merino ewes, whose breeding season begin in October/November, and twenty crossbred Mutton Merino x Border Leicester ewes, whose breeding season begin in February, lambed during the second half of October. Half of each group suckled single lambs for 6 weeks and half for 13-15 weeks. The post-partum interval to first oestrus was determined by using teaser rams. The crossbred ewes showed first oestrus at the usual time at the beginning of the breeding season and there was no difference in mean postpartum interval resulting from differences in length of lactation. The Mutton Merino ewes which suckled lambs for 6 weeks showed first oestrus in 87,7 ± 21,7 days, vs. 93,1 ± 19,6 days in ewes which suckled for 13-15 weeks. The difference between these means was not significant, but 80 % of the ewes which suckled for the shorter period showed oestrus within 100 days of lambing, vs. 40 %of those suckling for 13-15 weeks. The remaining ewes in the latter group were in oestrus within 1 cycle length of weaning. It is concluded that in ewes which lactate for a maximum of about 3 months and which are adequately fed, lactation anoestrus is of little practical significance. The season of lambing in relation to the breeding season appears to be of far greater importance.