Addressing these questions is specifically enabled by the Probes & Drugs portal (P&D, ). P&D was designed as a hub for the integration of high-quality bioactive compound sets enabling their analysis and comparison. As the name indicates, the main focus is on probes and drugs but includes additional relevant sets extracted from, or supplied by, recently published specialist databases (e.g. BiasDB ), vendor sets, supplementary data from papers (e.g. kinase inhibitors) or harvested from publication out-links (e.g. the British Journal of Pharmacology "Concise Guide" series ). Other high-quality curated bioactive chemistry sources, including ChEMBL 27 , BindingDB , Guide To Pharmacology (GtoPdb) , DrugCentral and DrugBank are utilized for compound biological annotation (the latter 3 are also P&D compound sets). The P&D compound database is currently composed of 69 sources including 12 probe-related, 7 drug compilations, 36 academic (non-commercial) sets and 14 precompiled sets from bioactive compound vendors (suggestions for expansion are welcome).