The paper reports the morphological and functional aspects of NK and K cells in the light of the most recent advances in the field, and pays particular attention to their cytotoxic and suppressor capacities. The role of NK and K cells in periodontal disease is then described and it is observed how this cell population is absent in healthy gums, whereas it is found with increasing frequency at disease reaches the chronic stage. The presence of LGL cells is therefore thought to be associated with the development of plaque-induced inflammation.