Finally the most important question concerns the contamination status of cell lines in culture collections, because many cell lines have existed for many years in these collections and might have been contaminated in periods when no or fewer tests were performed for proving the absence of BVDV. The question most relevant to the use of fetal calf serum for animal cell culture and animal cell culture technology is: which cells are/were contaminated by BVDV and are the cells from different species as easily contaminated as bovine cells or is there any species barrier. In this context, Bolin et al. (1994) performed a survey of cell lines from the American Type Culture Collection and observed the following contamination status: Using immunocytochemical procedures and PCR amplification, 13 of 41 ATCC cell lines were tested BVDV positive: these cell lines were derived from cattle, sheep, goat, deer, bison, rabbit, and domestic cat. Attemps to experimentally infect 14 different cell lines from animals, which were not found positive in the survey of the ATCC cell lines, led to the result that all swine cell lines (3/3: MPK, ESK-4, and one other) and most rabbit (3 out of 4: Sf 1 Ep, R9AB, RAB-9) and cat cell lines (3 out of 4: CRFK, AK-D, NCE-F161) became infected with BVDV, whereas hamster (BHK-21), human (IMR-90), dog (MDCK), rabbit (SIRC) and cat (Fc3Tg) cells were refractory to BVDV infections. The results concerning monkey cells (LLC MK2) were variable -no clear answer was obtained. Wessman and Levings (1999) reported that the following cell lines could be infected with BVDV: bovine cells (EBK, MDBK, BoTur, primary and continuous kidney cell lines, lung, trachea, and aortic endothe-lium), sheep choroid plexus and lamb kidney cells, monkey kidney cells (Vero and others), mosquito cells, porcine cells (PK-15 and others, testis, minipig kidney cells), goat cells (kidney and oesophagus), cat cells (lung, CRFK, tongue, feline embryo), rabbit kidney cells (RK-13), and others. Harasawa and Mizusawa (1995) published a study on the pestivirus contamination of cell stocks of the Japanese Cancer Research Resources Bank. Fifteen out of 20 cell lines (75%) were positive using RT-PCR. Whereas bovine cell lines (HH, MDBK, CPA, CPAE, EBTr, Ch1Es) were contaminated with genotypes I, II, and III, cell lines of dog, cat, and primate origin were contaminated with genotype II of BVDV (HeLa, MOLT-4, U937, WI-38, WiDr, CV-1, Vero, MDCK, CRFK). Roehe and Edwards (1994) assessed the ability of 11 pestiviruses from pig, eight from cattle, and five from sheep to replicate in cells of porcine (PK-15), bovine (BT) and ovine (SCP) origin. The pattern of replication in different cell types varied between different isolates of the same virus species.