Fibrinogen has long been used diagnostically as a positive acute phase protein in horses. Fibrinogen heterogeneity has been observed in humans and can influence fibrinogen measurements when using the modified Clauss assay. To date, no studies have evaluated fibrinogen heterogeneity in other species. In this thesis we investigate the existence of fibrinogen heterogeneity in horses, and evaluate the precision of a method for fibrinogen fraction purification and relative quantification. Lastly, we evaluate the stability of fibrinogen fractions with freezing.