When we compared serologic results with those of PCR, we found a profound difference between NPA PCR results and serum PCR results. Although results of serodiagnosis were identical to results of serum analysis by PCR, only 71% of NPA-positive children and 6% of NPA-negative children had an HBoV serodiagnosis. However, all but 1 (96%) of the children with a high load of HBoV DNA in NPAs had a serodiagnosis, compared with only 38% of those with a low DNA load. This finding supports the view that a low HBoV DNA load is not evidence of acute primary infection (10, 11, 31, 32) . Studies of consecutive NPA samples have shown that HBoV DNA can persist in the nasopharynx for several months (9, 33) . We also noted that 22% of children with HBoV DNA in their first serum sample continued to show viremia (with 2 logs less DNA) in the second serum sample obtained an average of 19 days later. That HBoV does not often persist in serum indicates that regardless of its magnitude, viremia is an excellent marker of acute HBoV infection.