The Unified Medical Language System (UMLS) is an extensive collection of terms and concepts. The UMLS includes biomedical terms from standard classifications. The semantic network (SN) links the concepts, sometimes ambiguously. In this paper we try, on one hand to describe the relationship between concepts more efficiently and on the other hand to find new relationships. Assuming that re-usability and automatic extraction of knowledge from existing thesaurus enables an improvement of the metathesaurus, we cross the SN with linked concepts from the ADM (Assisted Medical Diagnosis). Results are presented and our discussion concerns firstly the use of the SN only; secondly the improvement that allows pre-selection of linked concepts, and thirdly the possibility to coincide with other developments that improve the metathesaurus.