The influence of two scenarios of mortality rates (assumed average and observed) on total herd efficiency of the four main breed types in South Africa (Sanga/Zebu, composite, British and European), as well as all the individual breeds participating in the National Beef Performance Testing Scheme (1980-1985), was investigated by means of a computer simulation program. Simulation runs were done for an 18/18 month production system (all market animals sold at 18 months of age) in the case of the evaluation of breed types and for an 8/18 month (steers sold at eight months of age/ surplus heifers sold at 18 months of age), as well as an 18/18 month production system in the case of the evaluation of the individual breeds. Mortality rate had a marked influence on ranking of breed types as well as individual breeds in terms of relative income per hectare. Composite breed types normally performed well, indicating that use of such breeds in a variety of environments is a good choice. This study also indicated that bio-diversity does exist between breeds and further research is needed on breed characterization, since no framework currently exists for the characterization of breeds for bio-economic important traits.