The purpose of this contract is to provide research support for improving the structures, algorithms, methods, and procedures for maintaining and enhancing the United Medical Language System (UMLS) Metathesaurus. The Metathesaurus is a complex machine-readable knowledge source containing concepts and terms from a variety of biomedical terminologies and classifications. It is a tool for facilitating information retrieval from disparate machine readable sources, such as patient records and bibliographic databases, and a vehicle for uniform distribution of different vocabularies used in health data and information.