The Toxicology in the 21st Century (Tox21) program is a federal collaboration that uses automated high throughput screening (HTS) methods to quickly and efficiently test chemicals for activity across a battery of assays that target cellular processes. These assays rapidly evaluate large numbers of chemicals to provide insight on potential human health effects.
This data domain is part of Chemical Effects in Biological Systems (CEBS) database maintained by the National Toxicology Program.
At the link provided is a PDF and one or more folders containing data. The PDF describes the data, file types, and folder structure present.