Whilst high-throughput screening (HTS) has been the starting point for many successful drug discovery programs the cost of screening, the accessibility of a large diverse sample collection, or throughput of the primary assay may preclude HTS as a starting point and identification of a smaller selection of compounds with a higher probability of being a hit may be desired. Directed or Virtual screening is a computational technique used in drug discovery research designed to identify potential hits for evaluation in primary assays. It involves the rapid in silico assessment of large libraries of chemical structures in order to identify those structures that most likely to be active against a drug target. The key question is then how many molecules do you select from your virtual screen?

Whilst virtual screening is certainly less expensive than high-throughput screening it is not free, even an in house academic cluster has an overhead (probably equating to > $10,000 per virtual screen). So with that investment how much would you invest in actual compounds?