From the National Center for Biotechnology Information (NCBI), "PubChem contains the chemical structures of small organic molecules and information on their biological activities. It is intended to support the Molecular Libraries and Imaging component of the NIH Roadmap Initiative." PubChem users can search the chemical structure database by chemical properties, structural similarity, and descriptive terms. PubChem utilizes three connected databases--PubChem Compound, PubChem Substance, and PubChem BioAssay--all of which operate inside the Entrez/PubMed information retrieval system. In addition, the site offers the PubChem Structure Search tool for quick similarity searches. The site also links to contact information for the Structure Group research staff, and selected online publications.