Many common human diseases have a multifactorial origin: they are influenced by a person's genetic predisposition as well as by factors in the environment. This volume deals with the application of recombinant DNA techniques to the identification of diseases that have more than one inherited component. Focus is on the polygenic factors responsible for coronary atherosclerosis. Several other disorders having a polygenic origin are also discussed, including hypertension, diabetes mellitus, psychiatric diseases, and autoimmune (HLA-related) disorders. Problems raised by the study of different families or different populations are covered, as well as the possibility of applying molecular techniques to disease prevention—for example, through gene therapy. Also, some of the ethical issues that relate to human gene mapping are briefly explored.