Since its first description in 1981 (1), transgenic technology has greatly influenced the fetus and direction pace of biomedical research. Introduction of foreign DNA into the genome of animals by microinjection into fertilized oocytes is now used in almost every field of research spanning from oncology, immunology and neurology to cardiovascular medicine. The ability to integrate genes in the germline and their successful expression in the host provides an opportunity to study the role of a certain gene in the initation and propagation of disease. Transgenic methodology serves as the link between molecular biology, introducing in vitro a defined genetic modification and whole animal physiology, with the resulting in vivo alteration of body function. This potential has been exploited to study the pathophysiological role of human genes. Transgenic animals have been used to study aspects of tumor development, immune regulation, cardiovascular development and atherosclerosis. These studies have provided new insights into the genetic origin of certain diseases and have improved our understanding of pathological processes on the cellular level. As a future goal, these studies may also serve the development of new diagnostic tools or novel therapeutic strategies such as gene therapy.