Replication of HHV-6 in SAS413 and SAS527. HHV-6–inoculated SAS413 and SAS527 were observed with an inverted microscope to detect CPE (A) and analyzed by indirect immunofluorescence with HHV-6–seropositive human serum (B). Analyses were performed at day 6 of virus inoculation for HHV-6A–inoculated SAS413 and at day 240 for HHV-6B–inoculated SAS413, HHV-6A–inoculated SAS527, and HHV-6B–inoculated SAS527.