Human milk has many unique properties that benefit the breast-fed infant. Several of these attributes reside in the protein fraction of human milk, e.g., host defense factors such as immunoglobulins, lysozyme and lactoferrin, or digestive enzymes, specific binding proteins and growth factors. 1 , 2 These components are present either as soluble proteins in the whey fraction or as casein micelles. In addition, about 5% of total protein is bound within the fat globule membrane.