To evaluate the performance of the assay clustering method (described in section "Assay clustering" below), we annotated biological assays from a small subset of the data. For this purpose, all assays (2476) from the 4 human adenosine receptors (ARs) were collected: AA1R (P30542), AA2AR (P29274), AA2BR (P29275), and AA3R (P0DMS8). This subset was deemed small enough for manual annotation and at the same time representative for binding and functional assays recorded in ChEMBL as it includes a variety of different experiments. We labeled the meta target and the detection technology of these assays based on the assay description using subcategorizations previously described in literature. To speed up manual categorization, keywords relating to radioligands, fluorescence methods and functional responses were used for classification. The resulting label frequencies are shown in Table 1 and indicate that out of the 13 meta targets the most frequent ones include ligand displacement and cyclic adenosine monophosphate (cAMP) assays, whereas other labels occur less frequently.