To realize the potential of the Internet as a source of valuable healthcare information, for the general public, patients or practitioners, it is imperative to establish a validation system based on standards of quality. The WRAPIN project (World-wide online Reliable Advice to Patients and Individuals) from the European Community has this ambitious goal. WRAPIN is a federating system for medical information with an editorial policy of intelligently sharing quality and professional information. The WRAPIN project has two main axes: the efficient and intelligent search of information and the assertion of the trustworthiness of content. This article presents the scientific challenges involved in extracting the knowledge from text-based information in order to better manage the knowledge and the rest of the retrieval proc-ess. Our innovative approach is to efficiently extract MeSH terms from the analyzed documents exploiting UMLS knowledge sources. A benefit has been measured when comparing extraction results. Even if the evaluation is made with a limited corpus, this research work proposes heuristics that can be validated to the whole biomedical domain, and possibly enhanced by the adjunction of other methods.