Contamination problems associated with the use of serum Bovine serum might be contaminated by many different bovine viruses. Although theoretically qualitycontrolled serum should have been tested for all possible viruses, this is not possible for economic reasons and may not even be necessary. It is evident that each serum batch has to be tested for those viruses which are ubiquitous and known risks, such as the Bovine Viral Diarrhoea Virus (BVDV). However, there is also the question of the geographical origin of the serum which may indicate the need for additional virus tests. It is only necessary to test for those viruses, which are present in the geographical region from which the serum is coming. Table IX presents bovine viruses for which tests have to be performed depending on the geographical origin of the serum. The testing Table IX . Specific tests applicable to the screening of calf serum and porcine trypsin used for the production of medicinal products for human use (Eloit, 1999) Calf serum Trypsin (Table X) . In the following, the most important bovine viruses are presented in more detail.