The kinetics of Epstein-Barr virus (EBV) load was measured in peripheral blood mononuclear cells of a severely immunocompromised allogeneic bone marrow recipient child, in conditions not associated with lymphoproliferative disease. The viral doubling time was 46.4 hr. The study permitted monitoring EBV clearance from blood, when the anti-rejection therapy was interrupted. Likely, this is the first accurate kinetic assessment of EBV load increasing phase in a clinical context marked by the absence of an overt post-transplant lymphoproliferative disease. According to these data gamma-herpesviruses behave like beta-herpesviruses in being capable of rapid growth.