Incident to his routine diagnostic and interventional activities, the angiographer is becoming increasingly involved in the manipulation of blood clotting factors. Since the field of hemostasis generally extends beyond the sphere of conventional angiographic training, an analysis of selected angiographic aspects was undertaken. This paper reviews and summarizes the fundamentals of coagulation, and appropriate methods for manipulating coagulation during angiography, particularly via heparin and protamine sulfate. Basic aspects of platelet activity, and modifications produced by aspirin and dipyridamole, have been emphasized. Finally, the nature of the fibrinolytic system, and the current role of systemic and selective fibrinolytic therapy have been depicted.