80-90% of the adult population is known to have neutralizing antibodies to herpes simplex virus type 1 (HSV1), of these 18-32% suffer from occasional recurrent herpes labialis (RHL). It is thought that local trigger factors as external traumata, UV-light and chemical stimuli, or systemic factors like fever or common cold, may induce RHL. The aim of the present study was to investigate the frequency of RHL in a military brass band and compare this with the frequency of the disease in a control population of soldiers from the same unit. Both populations were national servicemen aged 19-22 yr. The diagnosis of RHL was based on the presence of herpetic vesicles in the labial region. Of the diagnosed cases, 10% were confirmed by laboratory procedures according to standard methods. The incidence of RHL over a period of 8 months was twice as frequent in the group of brass and woodwind players as in the control group of soldiers from the same military unit. This may indicate that the mechanical trauma to the labial tissue which occurs during playing may cause the increased frequency of RHL in musicians.