Platelet aggregometry has been the reference method employed to detect, diagnose, and monitor qualitative platelet disorders since the early 1960s. Lumiaggregometry and impedance-based whole blood lumiaggregometry have advantages over light transmittance aggregometry in that they provide for enhanced specimen management and increase the test sensitivity to impairment of platelet granule secretion. Whole blood lumiaggregometry detects and identifies congenital and acquired platelet plasma membrane receptor defects, metabolic pathway secretion disorders, and storage pool deficiency. Whole blood lumiaggregometry is also being applied to antiplatelet therapy monitoring and identifies aspirin and thienopyridine resistance. There is growing interest in using impedance-based whole blood lumiaggregometry for near-patient whole blood platelet analysis and antiplatelet therapy monitoring. This article will also discuss other whole blood testing processes for assessing platelet function, particularly as applied to assessing the effect of antiplatelet medication.