Quertle is a free semantic-based search engine for biomedical information (PubMed/MEDLINE, full-text articles, TOXLINE, grant applications, news, and whitepapers). Using advanced linquistics and natural language processing, Quertle is able to find meaningful conceptual relationships (such as 'A regulates B', or 'C is caused by D') in documents, not just the query terms scattered throughout a document. Quertle's unique Power Terms (which represent entire classes of related concepts, such as 'diseases') allow the user to answer real questions, for instance 'what chemicals cause diabetes'. Quertle also automatically determines key concepts and provides an easy-to-use interface, dramatically reducing the time and effort required to understand the literature.