Biomol Known Bioactives 2012 is based on the ICCB-Longwood Bioactives 1 collection (PL-0684-0685). This collection is nearly identical to the compounds that were in the high concentration of plates 1361-1362, plates 1791-1792 and 1989-1990 (4 compound difference). It was assembled by BIOMOL, working together with ICCB-Longwood, to provide a library of compounds that affect a wide variety of biological pathways relevant to ICCB-Longwood screening projects. The collection includes many classes of compounds including ion channel blockers, GPCR ligands, second messenger modulators, nuclear receptor ligands, actin and tubulin ligands, kinase inhibitors, protease inhibitors, gene regulation agents, lipid biosynthesis inhibitors, as well as other well-characterized compounds that perturb cell pathways. We hope this collection will help both in assay development and in target identification. Because the compounds are plated at a high concentration, we suggest these 2 plates are not the first ones screened when an assay is initiated at ICCB-L.