Six hundred Merino ewes were mated annually in March / April from 1962 to 1978 at the Carnarvon Experimental Farm. A total of 9 509 matings were done. On average, 12% of the ewes were not served as a result of the fact that a high percentage of the 2 year old ewes (34%) and 3 year old ewes (12%) were not served. Sixteen percent of the ewes that were served, failed to lamb. No age effect was observed. On average 14% of the lambs born were twins and 86 % of all the lambs survived from birth to weaning. On average 70 lambs were weaned per 100 ewes mated. A curvilinear correlation between the age of the ewe and weaning percentage was found, the 6 year old ewes being the most fertile.