The Metathesaurus of the Unified Medical Language System (UMLS) offers the possibility of mapping between various medical vocabularies. The Primary Care Electronic Library (PCEL) contains a database of over six thousand Medical Subject Headings (MeSH terms) describing the resources of the electronic library. We were interested to know if it was possible to map from MeSH to the Systemized Nomenclature of Medicine Clinical Terms (SNOMED CT). Such a mapping would aid healthcare professionals to retrieve relevant data from our digital library as it would enable links between clinical systems and indexed material.