ChemBank is a public, web-based informatics environment created by the Broad Institute's Chemical Biology Program and funded in large part by the National Cancer Institute's Initiative for Chemical Genetics (ICG). This knowledge environment includes freely available data derived from small molecules and small-molecule screens, and resources for studying the data such that biological and medical insights can be gained from their results. ChemBank is intended to guide chemists synthesizing novel compounds or libraries, to assist biologists searching for small molecules that perturb specific biological processes, and to catalyze the process by which new and effective medicines are discovered. ChemBank stores an increasingly varied set of cell measurements derived from various biological objects, including cell lines treated with small molecules. Analysis tools are available and are being developed that allow the relationships between cell states, cell measurements, and small molecules to be determined. Small molecules contained with ChemBank are manually annotated with biological activities from the primary literature using both internal and publicly available controlled vocabularies such as Medical Subject Headings (MeSH) and the Gene Ontology (GO). Currently, ChemBank stores information on hundreds of thousands of small molecules and hundreds of biomedically relevant assays that have been performed at the ICG in collaborations involving biomedical researchers worldwide. These scientists have agreed to perform their experiments in an open data-sharing environment. The primary goal of ChemBank is to provide life scientists unfettered access to biomedically relevant data and tools heretofore available almost exclusively in the private sector. ChemBank is intended to be a planning and discovery tool for chemists and biologists, as well as those interested in finding new therapeutic drugs. In sum, ChemBank is an evolving knowledge environment that can be freely used to extract knowledge from public experiments whose greatest value is likely to reside in their collective sum.