Human parvovirus, PARV4 was identified in a plasma sample from a patient presenting with symptoms resembling acute HIV infection. Further strains of PARV4 and those of a closely related variant virus, were identified in plasma pools used in the manufacture of blood derivatives. DNA sequence analysis of these strains demonstrated two distinct PARV4 genotypes. It has subsequently been proposed that transmission of PARV4 occurs by parenteral routes. To investigate the risk of contamination of plasma-derived coagulation factor concentrates, we analysed 169 lots for PARV4 DNA by polymerase chain reaction. Positive samples were confirmed by nucleotide sequence analysis and quantification of the viral load. Twenty-one lots, representing eight different products were administered until the beginning of the 1980s and were not virally inactivated. Two lots examined were used in 1997, and 146 lots representing 13 products had been administered between October 2000 and February 2003. PARV4 DNA was detected in 7(33%) of the formerly administered lots, in one lot used in 1997, and in 13(9%) recently used lots. PARV4 genotype 2 DNA was predominantly present in the older concentrates, whilst genotype 1 was found more frequently in recently used lots. In three lots, both PARV4 genotypes were detected. Viral loads ranged between <100 and 10(5.8) copies mL(-1) of product, with higher viral loads in the older concentrates. The results show that PARV4 contamination can be detected in an appreciable proportion of clotting factor concentrates. Further studies are needed to determine whether or not PARV4 contamination of coagulation factors causes harm to the product recipients.