Blood-serum concentrations of antibodies to such viruses as herpes simplex virus, cytomegalovirus and Epstein--Barr virus have been assayed versus frequency of viral DNA detection in blood and saliva suspensions from patients with lung and stomach pre-cancers. Condition of local immunity of oral mucosa was assessed on the basis of saliva levels of secretory IgA and lysozyme. It was found that as local immunity of oral mucosa deteriorated, irrespective of pre-cancer localization, high titers of antiviral antibodies (class G) were established. The frequency of herpes DNA was much higher in lymphocytes and cellular sediment from saliva of patients with gastric pre-cancers. The role of herpes viruses in the pathogenesis of precancerous diseases and malignances is discussed.