The advent of transgenic technology, in which foreign genetic information is stably introduced into the mammalian germ line, has dramatically enhanced our basic knowledge of physiologic and pathologic processes. Transgenic animals created by these genetic manipulations are being used to provide insights into gene regulation, development, pathogenesis, and the treatment of disease. Furthermore, transgenic biotechnology holds great promise for the creation of genetically superior livestock and the industrial production of precious pharmaceuticals. It is evident now that the study and use of transgenic animals will significantly improve the human condition.