The HBoV IgG EIA was conducted as described for parvovirus B19 (18) except that biotinylated VLPs were used at concentrations of 60 ng/well. Cutoff values were calculated from IgG EIA absorbances of the first serum sample obtained at admission of 34 children who had no IgM or maternal (waning) IgG against HBoV and showed a >4-fold increase of IgG against HBoV during follow-up testing. Cutoff absorbances for negative and positive IgG EIA results were 0.154 (mean + 3 SD) and 0.188 (mean + 4 SD), respectively.