Described is a method of targeting specific genes to the mammary gland which results in the efficient synthesis and secretion of biologically important molecules. Further, there is described as a composition of matter, a transgenic mammal having the ability to reproduce itself and being suitable for the secretion of biologically active agents into its milk. Additionally there is disclosed as a composition of matter, recombinant DNA gene complexes designed to integrate into a mammalian genome and to synthesize and secrete biological active agents into the milk. Furthermore, methods of producing and using altered milk are disclosed.