Antibacterial activity of the oral polymorphonuclear leukocytes and in vitro virus absorption by oral lymphocytes was studied in two patient groups and in controls. A slight decrease of phagocytosis was observed in those control cases and periodontitis patients where orolymphocytes and oral epithelial cells had absorbed viruses, but in the same subjects the bactericidal effect was significantly weaker. Periodontosis patients with a defect of polymorphonuclear cells did not exhibit such a difference. As in similar subjects the antibacterial activity was more frequently weak when their orolymphocytes carried latent viruses, the results suggest that certain individuals are prone to carry latent viruses in their lymphocytes. Lymphokines released from these carrier cells and concentrated locally might damage phagocytic leukocytes, resulting in serious local inflammation.