ABSTRACT In 7 of 18 solid-organ transplant recipients with primary human cytomegalovirus (HCMV) infection, HCMV antigenemia levels were unexpectedly found to rise significantly ( P = 0.018) during a mean time of 7.3 ± 3.2 days after initiation of specific antiviral treatment, whereas corresponding levels of viremia dropped significantly ( P = 0.043). Thus, shifting to an alternative antiviral drug based solely on increasing antigenemia levels is not justified in this group of patients.