A new method of measuring and analyzing the clinically significant structural characteristics of blood clots is described, using an oscillatory flow instrument (Vilastic-3 Viscoelasticity Analyzer). The development of the viscous and elastic properties of the clot are monitored continuously at known levels of stress and strain in a cylindrical tube [1], and specific transitional events and their timing are obtained. In clinical practice, two types of clot analysis currently are in use. One measures the time required for the clot to reach some instrument-determined degree of development, which provides no information about the mechanical character of the clot. The second yields a continuous depiction of the way the forming clot affects the instrument [2] and gives numerical values that are inseparable from instrument characteristics. For greater universality, it is preferable to obtain the clot properties per se, as opposed to integrated clot-instrument parameters, and to document the timing of well-defined viscoelastic events. Measurements on clotting blood and plasma show that the dependence of clotting characteristics on measurements conditions and hence the need for precise control of stress or strain during the process.