Platelets and fibrin play an important role in the coagulation process, where they are involved in the maintenance of hemostasis. Fibrin dysfunction is associated with the development of vascular complications, while proneness to the formation of tight and rigid fibrin networks is independently associated with thrombotic disease. Here we investigate the ultrastructure of human, rabbit, and mouse platelets and fibrin networks, using the scanning electron microscope. Human and rabbit fibrin and platelets, with regards to morphology as well as size of major and minor fibers compare well with each other. However, mouse fibers are much thinner and form a flimsy branching network. Platelet aggregate morphology of all three species compare well with each other. We conclude that rabbit platelet and fibrin networks could be used successfully when studying the effect of pharmaceutical products in preclinical trials, when looking at the effects of these products on morphology and ultrastructure. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc.