Protein nutrition has a great economic importance, since protein is an expensive item in almost all feed rations. This may particularly be so in areas of the world known to be protein deficient, such as many tropical and subtropical areas. The rationing of feeds for protein should, therefore, be manipulated in such a way that “optimal” rather than “maximum” performance is achieved without too much feed expenditure. The best way to explain this point is by a practical example of a layer feed with 16% or 17% protein. In corn-soybean diets, this difference can be created by adding 3% more soybean containing 44% crude protein. When this amount replaces corn, there will be an additional cost of about US$ 3.00/tonne world market price). In most cases, he real nutritional benefit of such an increase of protein is limited to an increase of about 0.025% of the amino acids lysine and methionine. The same nutritional advantage can be obtained by adding 250 g of synthetic lysine and methionine/tonne of feed with a cost of only US$ 1.00/tonne. Fortunately, access to these synthetic amino acids has become available with the recent advancement of biotechnology, which makes the economical benefits of such an approach quite achievable.