To determine the age at which a natural infection of turkey herpesvirus (HVT) occurs in turkeys, two studies were set up. A first study was performed on 6 Belgian turkey farms. On each farm, 20 turkeys were bled at two-week intervals, starting at the age of 7 days and ending at the age of 18 weeks, and the collected sera were examined for the presence of antibodies against HVT. Maternally derived antibodies, which were uniformly present at hatching, decreased during the first weeks of life and disappeared by the time the turkeys were five weeks old. An increase in anti-HVT antibodies was detected one week later. In a second study, 7-day old specific-pathogen free turkeys were inoculated intranasally with a Belgian HVT strain. Antibodies appeared 5 weeks after inoculation. From the serological data obtained in the two studies, it was concluded that a natural infection of HVT takes shortly after hatching, within the first days of life.