PubChem (http://pubchem.ncbi.nlm.nih.gov) is a public repository for chemical structures and their biological test results hosted by the U.S.National Institutes of Health (NIH).It was created as part of the research program under the NIH Molecular Libraries Program (MLP).The goal of MLP is to offer biomedical researchers access to the large-scale screening capacity and to discover chemical probes which may be used to modulate activity of gene products.PubChem contains three related databases:Substance,Compound and BioAssay for archiving contributed substance sample descriptions,unique chemical structures and bioactivity results.PubChems contents are currently derived from the voluntary contributions of over 90 commercial,academic and government organizations,with the majority of biological test results contributed by the MLP funded laboratories.PubChem currently contains 70 million chemical substance records,representing more than 37 million unique chemical structures.