Quantitative real-time PCR is being widely used in the identification of plasma donations that contain high levels of parvovirus B19, to ensure their exclusion from start pools used in the manufacture of plasma derived medicinal products. In this study, the primers and probe of one such published assay, are examined for their ability to quantify different genotypes of parvovirus B19. Under standard assay conditions, there is a failure to detect and quantify one genotype 3 subtype. Alterations in assay conditions can restore quantitation of this subtype.