Platelet-activating factor (PAF) is known to activate platelets and thus promote clot formation in most mammalian species including humans. In this communication, the ability of PAF to hasten the overall coagulation process by measuring the recalcification time (RT) is described. Assessment of the RT in vitro indicated that the RT was significantly reduced by PAF (p < 0.001). This information adds a new dimension to the role of PAF in coagulation and also provides an exciting lead to the development of drugs for controlling the state of accelerated coagulation by pharmacologic means.