With the addition of more potent antiplatelet and antithrombin therapies to the armamentarium of the treatment of acute coronary syndromes and percutaneous coronary interventions, monitoring these therapies has become an important interest. Current and evolving technologies to monitor the extent of inhibition of platelet aggregation and activity of factor Xa caused by IIb/IIIa antagonists and low-molecular-weight heparin, respectively, will be covered in this overview. An underlying question to be considered is whether the results generated from monitoring will effect a change that will improve the efficacy (prevent thrombotic events) or reduce adverse events (bleeding) from these potent therapies. (Am Heart J 2000;140:S136-42.)