Issues regarding the efficacy of feeding human milk to premature infants include the development of optimal protocols for collecting, storing, and processing human milk. Studies of the nutritional and immunologic composition of milk produced by women who delivered term or premature infants and who weaned their infants gradually from human milk have been studied to identify optimal donors. The effects of specific collection, storage, and processing conditions on the composition of mature human milk also have been evaluated. Collection, storage, and processing conditions have distinct effects on specific functional components. The caloric content of milk, the content of nutrients carried in the lipid portion of milk, and selected enzymatic activities depend on the completeness with which the breast is emptied. Storing milk in polyethylene, polypropylene, and pyrex containers influences key immunologic components in human milk as do storage temperatures. None of the nutrient compositions of milks studied matched current estimates of the nutritional needs of premature infants. Importantly, both the concentrations and the pattern of change in nutrient and immunologic contents are distinct in milks of women delivering infants at term or prematurely. Further changes are seen during the process of gradual weaning.