From NCBIannounce (http://www.ncbi.nlm.nih.gov/mailman/listinfo/ncbi-announce):
The PubChem Substance, Compound, and BioAssay databases are now available through the Entrez system. PubChem is a catalog of small organic molecules that contains chemical structures and information on biological activity. PubChem is intended to support the Molecular Libraries and Imaging component of the NIH Roadmap Initiative. PubChem's chemical structure database may be searched on the basis of descriptive terms, chemical properties, and structural similarity. When possible, PubChem's chemical structure records are linked to other NCBI databases, which include PubMed and NCBI's protein 3D structure database, for example. PubChem also contains the results of high-throughput biological screening experiments.