The 18K targets in PubChem include automated assignments that result in an element of overcounting. Those in the other three sources are classified by curators and have species-specific cross-references in UniProt . These give the following human Swiss-Prot counts of 3644, 2585 and 1,457 for ChEMBL, BindingDB and GtoPdb, respectively. We can see the document counts for the curated sources in column five of Table . From the ChEMBL release notes their literature extraction average out at ~15 compounds-per-document (n.b. the majority will have ARCP connectivity but some have only non-bioactivity A-R data such as plasma clearance).