The purpose of the present study was to compare the platelet and fibrin network ultrastructure of humans to eight different animal species in order to determine the differences between human and animal platelet and fibrin morphology, and to determine whether the animals studied differ in their platelet and fibrin morphology, and whether these differences can be observed by scanning electron microscopy. Platelets and fibrin networks play an important role both in the coagulation process as well as physiologically in allergic processes and immunological mechanisms. The thickness of human fibrin networks were compared to mouse (Mus musculus), equine (Equus caballus), vervet monkey (Chlorocebus aethiops previously Cercopithecus aethiops), oryx (Oryx gazella), ovine (Ovis aries), penguin (Spheniscus demersus), rabbit (Oryctolagus cuniculus) and sea turtle (Caretta caretta). Fibers were measured and divided into thin (minor) fibers, intermediate fibers and thick (major) fibers. The results obtained indicated that for each of the three fibrin classes, the size ranges of the monkey, oryx and equine were not significantly different to one another, and the human, penguin, oryx and ovine not significantly different to one other. From these results it can be concluded that mammals and aves possess a distinct tri-modal fibrin fiber distribution, different from that of the studied reptilian species where the sea turtle possesses a distinct bimodal fibrin fiber distribution and it can be suggested that the utilization of mammalian and avian models, in terms of fibrin fiber distribution patterns, might be a suitable alternative for ultrastructural studies.