The 67% inclusion in the MLSMR means these particular probes may have expanded profiling data from unpublished assays not captured by ChEMBL, including testing against malaria, other disease parasites and cancer cell lines (this is particularly the case for the older MLP compounds). The extensive data overlap between ChEMBL and BindingDB arises from their mirroring collaboration but the latter has unique content from patent SAR extractions. For some years GtoPdb has included probe curation from papers selected for their pharmacological relevance and this is reflected in the capture of 305 probes. The availability of a PDB ligand structure for 242 probes is clearly enabling for many reasons but note these may not all be for the probeprimary target pair or species. The explanation for the low hits to the Chemical Probes Portal was the inclusion of historical probes in their 2017 PubChem submission (we suggest the separate submission of this cautionary subset in the future). The last row in the table presents two anomalies. As discussed above, at least 100 additional nominal MLP probes can be found in various lists beyond the 223 in the PubChem CID select for "BioAssay, Probes". While reasons for the low match in P&D are being investigated the historical confusion associated with legacy MLP compounds may confound unequivocal explanation.