3 simulated breeding programmes (pure breeding, rotational crossbreeding and specialised sire ana dam lines) were compared in terms of the total T.D.N. required and beef produced in 9 successive yr, and the efficiency of T.D.N. utilisation for beef production. Each programme was assumed to have 1000 breeding ♀♀, calving first at 24 mth and thereafter at intervals of 12 mth, and a weaning percentage of 85. There was a 20% replacement rate and calves produced per cow averaged 4.5. It was also assumed that calves would either be sold as weaners at 6 mth or as yearlings. The type and live weights of cows in each system are described. It was concluded that the ranking of the 3 breeding systems depended primarily on the differences in size of the breeding ♀♀ in each system and the differences in inherent growth potential of their progeny. The rotational system used the heaviest cows, produced the most beef, required most T.O.N. and was more efficient than the purebred system but less efficient than the special cross system. The latter used the smallest cows mated to large bulls, and was the most efficient in terms of beef produced per unit T.D.N. required. These relationships among the breeding systems might vary if different assumptions were used for such traits as calving percentage, attrition rate and the value of cow and calf beef. It should also be remembered that the advantages of hybrid vigour were largely disregarded in this study. Hybrid vigour for fertility, growth rate and milk production would augment the advantages of the crossbred systems over the purebred programme.