Recently, a new group of viruses, the circoviridae, was described. The circoviridae are very small viruses (non-enveloped, circular single stranded DNA, diameter of 17 nm) and are very resistant against most of the inactivation methods currently used. This group of viruses was found in Japanese patients suffering from non A to G hepatitis, described as TT virus (Nishizawa et al. 1997) , and also found in chickens, where it is described as Chicken Anemia virus (Yuasa et al., 1979) . This virus seems to be ubiquitous in humans because DNA of the TT virus was identified in plasma of 76% of French blood donors (Biagini et al., 2000) . It is evident that such a virus might be a problem when human derived proteins are used, because this it is very resistant against most inactivation methods. Tischer et al. (1982) described a circovirus in pigs, and it has been reported that the swine cell line PK-15 was chronically contaminated by this type of virus. A serological study showed that 20 out of 22 randomly collected pig sera contained specific antibodies against the virus, whereas no specific antibodies could be detected in sera from rabbits, mice, calves, and man, including the laboratory staff working with this virus (Tischer et al., 1982) . The virus exists as 2 subtypes, type 2 porcine circovirus replicates actively in porcine fetuses (Sanchez et al., 2001) and is associated with abortions, reproductive failure and postweaning multisystemic wasting disease in swine (O'Connor et al., 2001; Ellis et al., 2001) , however, it seems that this virus is very porcine specific .