NK cells are important cells of the immune system derived from stem cells in the marrow. Their function in infectious diseases and pregnancy is controlled through a complex system of cell receptors to control cell proliferation, cytotoxicity and cytokines. The production of hormones and other pregnancy regulatory factors in primigravidae may alter cell function, thereby conferring an advantage for malaria infection. A causal relationship between high cortisol levels and depressed NK cell cytotoxicity against P. falciparum-parasitized erythrocytes and susceptibility to malaria has been demonstrated. Parasitized erythrocytes become sensitive to NK cytolysis and prolactin, and cortisol serum levels were related with NK cells cytolytic activity. Despite limited success in currently reported therapeutic trials, understanding the biology of NK cells and their homing mechanisms in vivo may lead to novel therapeutic strategies. However, much research remains to be done.