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There is some concern that methods of sire evaluation which utilize contemporary stablemate averages can be biased by differential genetic merit of the mates of these sires. A little reflection, however, indicates that even if the cows to which some sires are mated are more highly selected than the mates of other sires, this differential merit will not affect seriously the ranking of sires according to the evaluation of their progeny. Until the present, data have not been readily available with which to study the seriousness of this problem. The present study does not deal with the question generally, but attempts only to discover the effect of the estimated genetic merit of dams on the evaluation of three sires which were used in planned matings. The term "planned mating" as understood for this study refers to matings through artificial insemination to sires which are not normally available for service except by special request at additional cost and which are not owned by the distributing organization. The three sires whose matings are studied were from "popular" herds and were older bulls without an evaluation on the basis of their artificially sired progeny. Thus, a situation worse than would normally exist with respect to selected mates seems likely to exist.