High-throughput assays are important biological research tools but are rarely utilized for platelet research. However, screening compounds for efficacy against a physiologically relevant cellular response in primary cells such as platelets can be an advantageous approach to compound screening and drug development. In this section we describe a panel of three high-throughput microtiter plate assays designed for platelets that can be used as the basis for compound screening, or be modified and used individually to increase throughput in platelet research laboratories. The platelet adhesion assay has the lowest requirement for platelet numbers and is therefore capable of the greatest throughput and so is suggested as the primary screen used to identify hits. A secondary screen against the "gold standard" of platelet function, aggregation, is used to confirm and further characterize hits. Finally, a Ca2+ assay is used for initial mechanistic characterization to begin the process of elucidating the mode of action of hit compounds.