A test set was compiled which covers the 35 proteins with the highest number of CSMs (between 108 and 730) in the processed ChEMBL data set (Table ). Note that the delta opioid receptor from Mus musculus, the mu opioid receptor from Cavia porcellus and the mu opioid receptor from Homo sapiens were excluded from this selection because larger and/or more balanced sets of CSMs were available for the respective receptors from Rattus norvegicus. In addition, the protein "protease" from human immunodeficiency virus 1 (CHEMBL2366517) was excluded because of the availability of a more comprehensive set of data on the protein "human immunodeficiency virus type 1 protease" (CHEMBL243).