Wiltshire Horn-Merino (WH-M) and Border Leicester-Merino (BL-M) ewes, both with 50% Merino ancestry, were mated in late spring to lamb in 1985 and 1986 to either Dorset Horn (DH) or WH-M rams. Lambs from WH-M sires grew more slowly than lambs from DH sires, by 2 to 13% depending on dam breed and age of lamb. Lambs from WH-M dams grew 3 4 % slower than lambs from BL-M dams in 1985, a year of good pasture and with only DH rams used. In the following year, they grew at a similar rate from birth to weaning if from DH sires, but 11% more slowly if by WH-M sires. From weaning to turnoff, the ranking was reversed, with lambs from WH-M dams growing 11% faster, and sire breed not significant. When mated to DH rams, both the WH-M and BL-M ewes produced lambs with similar dressing percentages and fat depths over the 12th rib. Lambs sired by WH-M rams were leaner than those sired by DH rams, particularly for single-born lambs. The WH-M ewes tended to have a higher percentage of lambs marked per ewe joined than the BL-M ewes, but the advantage was not statistically significant. The difference was mainly due to fewer barren ewes, but the WH-M ewes also showed slightly higher prolificacy. The WH-M ewe shows good fertility and prolificacy, and when mated to a DH ram gives lambs with growth and carcase characteristics very similar to a BL-M identically mated. Mated to a WH-M ram, it gives slower growth but leaner carcases capable of being efficiently grown to heavier liveweights than conventional Australian 3-breed crosses.