With the development of the Unified Medical Language System (UMLS) Knowledge Sources, the National Library of Medicine (NLM) has produced a resource of great potential for improving the searching of MEDLINE. The Coach expert searcher system, an inhouse research project at NLM, is designed to help users of the GRATEFUL MED front-end software improve MEDLINE search and retrieval capabilities. This paper describes the Coach program, the knowledge sources it uses, and some of the ways it applies elements of the UMLS Metathesaurus to facilitate access to the biomedical literature.