The parvovirus PARV4 is the most recently described member of the family Parvoviridae that has a human host. To investigate the prevalence of PARV4 in blood, a quantitative TaqMan PCR was developed and plasma, sera or whole blood from a variety of population groups were examined. Eight samples were positive for PARV4, one at high copy number. The high-titre-positive plasma had an approximate viral load of 5×108 genome equivalents ml-1. Two human sera, identified as PARV4 antibody-positive by indirect immunofluorescence, were used in immune electron microscopy to try to visualize native PARV4 within the high-titre human plasma. PARV4 particles were observed using one of these two sera. To our knowledge, this is the first time that native PARV4 has been visualized.