The Protein Data Bank contains a large amount of proteins that have been solved with small ligands bound to them. This constitutes a rich source of information for the study of the specific requirements of protein sites to bind small molecules with a favorable free energy. The specific atomic composition and three-dimensional geometric restraints of protein binding sites for different ligands could be easily obtained from there. The development of accurate binding site descriptors in proteins constitutes a valuable tool to assist in the large-scale prediction and annotation of protein function in whole genomes. In this work, an integrated database containing some processed and calculated protein/ligand information is described. It is expected that this database will constitute a useful tool for people working in the prediction of protein function from its structure. The database is accessible from the Internet through a web server located at: http://protein.bio.puc.cl