Out of the 2.9 million binding data currently in BindingDB, the vast bulk, i.e., 2.4 million, are associated with human-derived protein targets. The next most represented source organisms are rat (177K data), mouse (65K), and human immunodeficiency virus type 1 (29K), followed by a long tail of ~560 additional source organisms with fewer and fewer binding data. Human-derived protein targets number 3,410. Table lists the 25 human-derived targets with the most data in BindingDB. These comprise primarily signaling kinases, cell-surface receptors, nuclear hormone receptors, and other enzymes. Most affinity data stored in BindingDB are reported and hence curated as IC50s (1.8 million), followed by Ki values (560K), EC50s (220K), and Kd values (100K). Interestingly, affinities curated from patents tend to be greater (stronger binding) than those from articles, as shown in Figure , with a ~10x lower mode in the distribution of IC50, Ki, or Kd values. In addition, molecular weights of compounds extracted from patents tend to be higher than those of compounds coming from articles (Figure ), with a mode of ~450 Da versus ~400 Da. These differences presumably reflect the fact that patents present more chemically elaborated ligands than those described in articles, which are more exploratory in character.