Secretion of Epstein-Barr virus (EBV) in saliva, as well as serum antibody titres against various EBV antigens, were analyzed in respect of (1) 15 HIV-1-infected patients with oral hairy leukoplakia proven to contain EBV by in situ hybridization, (2) 45 HIV-1 infected patients without hairy leukoplakia, (3) 10 HIV-1 infected patients treated with acyclovir or foscarnet and (4) 21 healthy controls. The numbers of CD4+ cells in the peripheral blood were also recorded. The HIV-1 infected patients were at various stages of HIV-1-associated disease. Excretion of EBV DNA in the saliva was determined by means of the polymerase chain reaction (PCR) while the amount of EBV DNA in positive samples was estimated by repeated titrations. The frequency of shedding of EBV DNA increased from 33% in healthy controls to 78% in asymptomatic HIV-1 infected persons, but did not increase significantly with progression of HIV-1-associated disease. The titres of EBV DNA in saliva correlated inversely and significantly with the number of CD4+ cells in the peripheral blood. All patients with hairy leukoplakia shed by EBV DNA in their saliva but the titres were not significantly higher than those of other HIV-1 infected persons. The serum titres of antibodies against EBV nuclear antigen 1 (EBNA-1) correlated positively and significantly with the CD4+ cell count in the peripheral blood. EBNA-1 IgG antibody in the serum was also significantly lower in symptomatic than in asymptomatic HIV-1 infected persons. There were, however, no significant differences in serum antibodies to various EBV antigens between patients with and without hairy leukoplakia.