* PubChemProvides information on the biological activities of small molecules: substance information, compound structures, and BioActivity data in three databases, PCsubstance, PCcompound, and PCBioAssay. The Substance/Compound database provides links to BioAssay description, literature, references, and assay data points. It links back to the Substance/Compound database, is integrated with Entrez, and provides compound neighboring, sub/superstructure, BioActivity data, and other search features.