In examining what sex ratio control might mean in the animal world from a positive viewpoint, one may ask “What are the advantages of sex control?” The answer most frequently given is that it permits the breeder to have what he wants. However, in practice, what the breeder and commercial producer of domestic animals, including poultry, want is the most efficient and profitable program. It is, perhaps, not surprising that little appears to have been published suggesting specifically what impact sex control might have on the production of milk, meat and eggs, considering the myriad of possibilities as well as the hazards of prediction. This paper will discuss several factors likely to be important in applying sex control, particularly to farm animals, and will give selected examples of its possible contribution to the production of food and other animal products. Throughout, we will assume that the sex ratio at birth (secondary sex ratio) is 50 ♂: 50 ♀, although it is known to deviate slightly from this for most species (Lawrence, 1941; Altman and Dittmer, 1962). Furthermore a variety of natural conditions has been reported to be associated with minor changes in the sex ratio (Lawrence, 1941), and some investigators have reported spurious deviations in sex ratio as a result of unfortunate classification of data. General Advantages and Limitations of Sex Ratio Control. Effective sex ratio control could permit producing the optimum proportion of males and females to take advantage of phenotypic differences in sex-limited traits, such as milk and