After many years of advocating the benefits that arise from the use of genetically superior or proven bulls, the principle has now found almost universal acceptance in the U.K. A study of the reports of Milk Recording Services shows the widening gap between the breeder using proven bulls and the one who does not and confirms theory with results in practice. It is perhaps easy to forget that this acceptance of the proven bull does not apply in many other countries. Finding and identifying the genetical superior sire is, however, a long and costly operation, particularly with the dairy breeds. Even with modern sophisticated methods of predicting breeding ability, it is unlikely that more than one sire in four tested will be returned to the stud for widespread use (M. M. B. Breeding and Production, 1977/78).