Human milk proteins are believed to have a multitude of biological activities benefiting the newborn infant. Such functions include antibacterial and antiviral activities, enhancement of the immune system and increased nutrient absorption. To date, only breast-fed infants have been exposed to these proteins. However, by using genetic engineering it is now possible to express these proteins in plants, such as rice, at very high levels. Recombinant human milk proteins can subsequently be added to infant formula and baby foods. Prior to such addition, safety tests and efficacy trials need to be conducted. The safety tests will initially be done in rats and then in humans. The efficacy trials should also evaluate stability against heat treatment (processing), pH (stomach conditions) and proteolytic enzymes (digestion). To date, we have expressed recombinant human lactoferrin, lysozyme and á1-antitrypsin in rice at very high expression levels. These recombinant proteins showed a stability and activities similar to those of the native milk proteins, suggesting that they may be able to exert biological activities in infants when added to formula or baby foods.