HIC-Up ('Hetero-compound Information Centre - Uppsala') is a repository of structure-related information about the small molecules (ligands, co-factors, ions, metal-clusters, etc.) that occur in complex with larger biomolecules in any of the structures deposited in the Protein Data Bank (PDB). For every compound, the database contains a subset of the following information: atomic coordinates, images, refinement dictionaries, and links to a number of other web sites that also provide information about the compound (e.g., PDB, PDBsum, EDS, PRODRG, Relibase, EBI-MSD Ligand Chemistry, Jena HCD, and NIST Chemistry Webbook). HIC-Up can be accessed through any web browser (http://xray.bmc.uu.se/hicup or a mirror site). In addition, the entire web site can be downloaded for local installation. The database is updated twice a year on average.