An expert assessment of striking recent developments in molecular genetics and their implications for medical practice at present and in the immediate future. Adopting a public health approach the report aims to help medical decision-makers and practitioners understand both the technical basis of progress and its potential to revolutionize the management of numerous diseases. Advances in the prevention and treatment of classical genetic disorders are considered together with newer opportunities opened by knowledge that many common disorders including coronary heart disease and certain cancers have a genetic component. Throughout the report a special effort is made to help planners in developing and developed countries alike reap the full public health benefits of technologies that are becoming increasingly powerful simple and inexpensive to use. Information ranges from a discussion of the state-of-the-art in gene therapy through a tabular summary of treatment results for specific congenital anomalies to advice on ways to integrate simple genetic approaches into everyday medical practice. Relevant ethical social and legal issues are also critically assessed in an effort to provide comprehensive guidance. The report has eight sections. Background information is provided in the first which explains the structure and functions of DNA summarizes knowledge about the genetic basis of both single-gene and multifactorial disorders and traces the spectacular development of DNA technology and diagnostic tests over the past decade. The Human Genome Project - and its potential to transform medical practice on many levels - are also explained in detail. A section on epidemiology discusses factors influencing the frequency of genetic and congenital disorders and describes opportunities for their management and prevention. The impact that these advances will have on the demand for genetic services is also assessed. The large scale of implications for medical practice is underscored in the third section which reviews and interprets growing knowledge about the genetic component of many common disorders including coronary heart disease certain cancers asthma diabetes mental disorders and Alzheimer disease. A comprehensive review of current and future opportunities for prevention including both genetic family studies and population screening is followed by sections covering the basic principles of genetic counseling and opportunities within the context of obstetric care for prenatal diagnosis using ultrasound scanning and DNA technology. The remaining sections offer advice on the organization of genetic services in industrialized and developing countries alike and discuss the ethical social and legal aspects of genetic technology in medicine concluding that the broadest ethical issue in the area of genetic services is their limited availability.