Sera from 118 children aged up to 4 years were tested by indirect immunofluorescence for human herpesvirus-6 and -7 (HHV-6 and HHV-7) antibodies. Antibody results were confirmed as true positives if the relevant viral DNA was detected in saliva or, in some cases of primary infection, by the finding of the relevant DNA in cerebrospinal fluid or serum. Results from samples taken from the 15 children less than 6 months old showed that HHV-6 and/or HHV-7 antibody was either absent or present at low titre suggesting persistent maternal antibody rather than true infection. The sensitivity, specificity, positive and negative predictive values of the HHV-6 IgG test were therefore based on the data from the 103 children older than 6 months and the results were 95, 84, 91 and 90%, respectively. Likewise, the sensitivity, specificity, positive and negative predictive values of the HHV-7 IgG test were 95, 76, 84 and 93%, respectively. There was limited cross-reactivity between HHV-6 and HHV-7 antibodies; where both HHV-6 and HHV-7 antibodies are detected, titres above 32 may be accepted as true positives but lower titres require confirmation by detection of the relevant viral DNA or, in the case of primary infection, by a rising antibody titre.