The National Library of Medicine: from MEDLARS to the sesquicentennial and beyond.

The two decades since the introduction of MEDLARS and the passage of the Medical Library Assistance Act have been especially eventful in the history of the National Library of Medicine. The library's collections and services have grown to keep pace with the expanding health sciences literature and the needs of health professionals. Networking has emerged as an invaluable method for disseminating biomedical information. NLM has assumed new responsibilities for information services in toxicology, pharmacology, and environmental health, and for research and development in biomedical communications. Research now being carried out by NLM has the potential for enhancing the library's archival programs and for improving information dissemination in support of health sciences research, education, and practice.