PubChem: Open Chemistry DatabasePubChem from the U.S. National Library of Medicine provides information on the biological activities of small molecules in three main databases: PcBioassay, PcCompound, adn PcSubstance. PubChem is integrated with Entrez, NCBI’s primary search engine, and also provides compound neighboring, sub/superstructure, structure, targets, BioActivity data, and patents. Contains information formerly found in ChemID Plus and the NLM Drug Information Portal.