Link to the National Library of Medicine (NLM). The NLM is located on the campus of the National Institutes of Health in Bethesda, Maryland, and is the world's largest medical library. The Library collects materials in all areas of biomedicine and health care, as well as works on biomedical aspects of technology, the humanities, and the physical, life, and social sciences. Housed within the Library is one of the world's finest medical history collections of old and rare medical works. The Library's collection may be consulted in the reading room or requested on inter-library loan. NLM is a national resource for all U.S. health science libraries through a National Network of Libraries of Medicine®. For more than 100 years, the Library has published the Index Medicus®, a monthly subject/author guide to articles in 3400 journals. This information, and much more, is today available in the database MEDLINE® via the World Wide Web. MEDLINE has more than 11 million journal article references and abstracts going back to the early sixties. Other databases provide information on monographs (books), audiovisual materials, and on such specialized subjects as toxicology, environmental health, and molecular biology. Through the Web at http://www.nlm.nih.gov some 250 million searches of MEDLINE are done each year by health professionals, scientists, librarians, and the public. There are increasing links between article references and full text, and a new service called PubMed Central will allow free access to a central repository of journal articles. The NLM has created a special Web site, MEDLINEplus, to link the general public to many sources of consumer health information. Research and Development is carried out by the Lister Hill National Center for Biomedical Communications (LHNCBC) and the National Center for Biotechnology Information (NCBI). The LHNCBC explores the uses of computer, communication, and audiovisual technologies to improve the organization, dissemination, and utilization of biomedical information. Currently the Center is applying modern communications technologies to health care-related projects involving, for example, telemedicine, test-bed networks, virtual reality, and a Unified Medical Language System. The Visible Human Project® has created, in complete anatomical detail, 3-dimensional representations of the male and female human body, resulting in a large digital image library. "Profiles in Science" is the Center's new Web site that provides access to the laboratory notes, photographs, and correspondence of notable American scientists. Established by Congress in 1988, the National Center for Biotechnology Information has assumed a leadership role in developing information services for biotechnology--the task of storing and making accessible the staggering amounts of data about the human genome resulting from genetic research at the NIH and laboratories around the nation. NCBI is a recognized leader in basic research in computational molecular biology, and is also responsible for developing innovative computer solutions for the management and dissemination of the rapidly growing volume of genome information. NCBI distributes GenBank®, a collection of all known DNA sequences, and also provides access to the assembled Human Genome data. Both are accessible at http://www.ncbi.nih.gov. Toxicology and Environmental Health Program (TEHIP), established at NLM in 1967, is charged with setting up computer databases from the literature and from files of governmental and nongovernmental organizations. TEHIP has implemented the TOXNET® (Toxicology Data Network) system of 10 data banks useful in chemical emergency response and other applications. TOXNET is searchable without charge on the Web. The Extramural Programs Division provides grants to support research in medical informatics, health information science, and biotechnology information, as well as for research training in these areas. Network planning and development grants support computer and communication systems in health institutions and the study of new opportunities with high-speed computer networks in the health sciences. Health science library resource grants assist in improving information access and services for health professionals. Research and publications in the history of medicine and the life sciences are also supported. The NLM's Unified Medical Language System (UMLS) project, http://www.nlm.nih.gov/research/umls/, develops and distributes multi-purpose, electronic "Knowledge Sources" and associated lexical programs. System developers can use the UMLS products to enhance their applications -- in systems focused on patient data, digital libraries, Web and bibliographic retrieval, natural language processing, and decision support. Researchers will find the UMLS products useful in investigating knowledge representation and retrieval questions.