All adherently growing cells have to be detached for passaging from time to time. To facilitate this the enzyme trypsin is frequently used. As for serum, trypsin is an animal derived product, generally from porcine pancreas. Therefore, similar safety criteria as for serum have to be applied for trypsin. A special concern is Porcine Parvovirus (PPV). Latent parvovirus contamination has been found in many permanent human cell lines. The first contamination was observed by Hallauer and Kronauer (1960) when they observed that some control cultures (non-infected with Yellow Fever virus) yielded a different hemagglutinating agent, unrelated to Yellow Fever virus, when subjected to their isotonic, high pH glycine extraction buffer (= physiological stress). Further studies identified this infectious agent as a member of the parvovirus group. Following this, Hallauer et al. (1971) isolated 38 parvoviruses in 43 permanent human cell lines obtained from 19 laboratories. Some cell lines showed signs of degenerescence when arriving into the laboratory of Hallauer, others appeared completely normal. Three different serotypes of parvovirus could be identified, the origin of them is not really known. However, the recovery of the same serotypes from different laboratories suggests a common source, such as a reagent used in cell cultivation. One of the serotypes had been identified as PPV, indicating that the use of contaminated trypsin lots was the probable source of contamination (Fikrig and Tattersall, 1992) . The definite proof that porcine trypsin was the source for cell culture contaminations by PPV was apported by Croghan et al. (1973) , because they detected the same serotype in commercial trypsin lots.