Rigel SCT is a SNOMED CT concept search service engine and corresponding user inteface. Rigel is designed to improve on extant SCT search facilities in a number of ways: extremely high-performance interactive search, with autocompletion, autosearch and match highlighting highly sensitive search, using lexical analysis highly specific search, via a context-sensitive match grade algorithm search filters, by hierarchy standard subset, including the CORE Problem List hypertree browsing of the SCT multihierarchy (Java version only) A more detailed description of Rigel functionality and system requirements can be found here. The Rigel UI is available in two client forms: Java and Web. The Java form is available for three languages and dialects: US English, GB English and Spanish, and includes a hyperbolic tree browser. Rigel uses the US SNOMED CT distribution, and the SPECIALIST Lexicon, both from the NLM.