The presence of human herpesvirus 6 (HHV-6) and human herpesvirus 7 (HHV-7) in throat swabs of 62 children of different age groups (group I, ages 0-5 month; group II, ages 6-11 months, group III, ages 12-23 months, group IV, age 2-8 years) and 28 adults was detected by polymerase chain reaction. The detection rate of HHV-6 DNA was the highest (87%) in children aged 1-year-old and decreased with age, whereas the detection rate of HHV-7 increased with age and reached a maximum in adults. HHV-6B was detected in almost all samples except for two children who secreted only HHV-6A. When the antibody prevalence was determined in the four groups of children, HHV-6 antibody was detected in 8/12 (66.7%), 10/12 (83.3%), 15/16 (93.8%), and 13/14 (92.9%), respectively. Antibody to HHV-7 in these groups was detected in 6/12 (50.0%), 4/12 (33.3%), 12/16 (75.0%), and 13/14 (92.9%), respectively. Detection of HHV-6 DNA in throat swabs of triplets who had the sequential onset of exanthem subitum was attempted by using samples sequentially collected from these children after the onset of the disease in the first patient. HHV-6 DNA with high copy numbers was detectable during the acute and convalescent phases of the disease in all patients, but no DNA was detected in samples collected before the onset of disease.