Both. SciFinder and Reaxys are complementary resources, and although both are ultimately based on the primary literature, they are quite different in the ways they scan and index the literature, the ways they register compounds and index reactions, and in the dates they cover. Reaxys is recommended for obtaining checked physico-chemical data, preparation/reaction methods, and especially for its near-comprehensive coverage of pre-1960 organic literature. Literature references in Beilstein and Gmelin go back to the 18th century. SciFinder excels with its very thorough coverage of the literature and patents from 1967 forward, its comprehensive registration of all types of chemical compounds and structures, and coverage of organic reactions after 1985. CAS also scans far more source journals than either Beilstein or Gmelin, and indexes new material more rapidly. For chemists interested in synthesis, reactions and chemical properties, it is always advisable to search both databases. For a s