INTRODUCTION: NK cells represent a distinct lymphocyte population with extensive cytolytic activity and a variety of other functions, including regulation of hemopoiesis, suppressor functions and immunoglobulin production. Recently, reports suggest that NK cells also display potent regulatory functions via secretion of cytokines or cell-contact-dependent mechanisms. Thus NK cells may regulate innate and adaptive immune responses and play a role in immune homeostasis. AREAS COVERED: NK cells play important roles in viral infections, autoimmunity, pregnancy, cancer and bone marrow transplantation. Although the role of NK cells in allergic diseases is poorly described, recent findings suggest their role in allergy. EXPERT OPINION: Recent developments in the study of NK cell subsets have support their role in allergic diseases that contribute to allergen-specific immune suppression, allergen-specific T(H)1 cell generation as well as IgE and other Ig production.