The variable response to antiplatelet therapy has led to the use of platelet function tests to monitor the effects of antiplatelet drugs in cardiovascular diseases. The goal is to guide antiplatelet therapy to the optimal dose for the prevention or treatment of thrombosis while minimizing hemorrhagic side effects. The bleeding time is no longer recommended for use because of its nonspecificity and lack of clinical correlations. The current de facto "gold standard" test of platelet function is turbidometric platelet aggregometry. Although this method has been successful in measuring the aggregation of platelets in a glycoprotein (GP) IIb/IIIa (integrin alpha(IIb)beta(3))-dependent manner, it has several limitations, including poor reproducibility, high sample volume, requirement for sample preparation, length of assay time, requirement for a skilled technician, and cost. Therefore, new options for platelet function testing have been developed to address these disadvantages and to meet the need for point-of-care testing that can be performed at or near a patient's bedside without requiring a high degree of technical expertise. The new tests include VerifyNow (Accumetrics, San Diego, CA); Plateletworks (Helena Laboratories, Beaumont, TX); Thrombelastograph PlateletMapping System (Haemoscope Corporation, Niles, IL); Impact cone and plate(let) analyzer (DiaMed, Cressier, Switzerland); and Platelet Function Analyzer 100 (PFA-100; Dade Behring, Newark, DE). In patients treated with antiplatelet drugs, the degree of platelet inhibition, as determined by several of these new platelet function assays, has been shown to predict major adverse cardiac events.