The objective of this chapter is to summarize and evaluate some of the most common chemoinformatic methods that are applied to the analysis of high-throughput-screening data. The chapter will briefly describe current high-throughput-screening practices and will stress how the major constraint on the application of chemoinformatics is often the quality of high-throughput-screening data. Discussion of the NCI dataset and how it differs from most high-throughputscreening datasets will be made to highlight this point.