Any biopharmaceutical product that has involved the use of animal-derived material during the manufacturing process has the potential to be contaminated with animal viruses. To ensure safety of these products, extensive testing is performed on the starting materials, such as the cell banks, and on the raw materials used in manufacture. Additional testing is also performed at various stages of production and, in some cases, on the final product as well. Because of inherent limitations in direct testing methods, the capacity of the downstream purification process to remove/inactivate potential viral contaminants is also studied to give an extra degree of assurance that the final product will be free of infectious viruses.