Serological markers of Epstein-Barr virus (EBV) infection has been inv
estigated in 28 patients with infectious endocarditis. In 75% of patie
nts IgM antibodies to ''early'' antigen of the virus which are the mar
ker of active viral infection occurred vs 6.2% among healthy blood don
ors. Specific for infectious endocarditis reaction profile (anti-EBV c
ombination in one person) indicates reactivation of latent viral infec
tion. The conclusion is made on the necessity of further investigation
of both the role of EBV in pathogenesis of pyoseptic diseases and imm
unologic mechanisms for reactivation of latent viral infections.