There have been no reports of HBV transmission during mouth to mouth. The best evidence comes from studies done in gibbons (monkeys). These studies showed that saliva from infected humans could infect the animals if injected either intravenously or under the skin (subcutaneously). Thus, HBV in saliva is potentially contagious or infectious. However, equally as important as this finding - the researcher were not able to transit HBV in saliva to mouth contact (i.e. exposure such as kissing).