Receptors for the constant or Fc part of IgG (Fc gamma R) constitute an important link between the humoral and cellular parts of our immune system. Fc gamma R expressed on leukocytes are capable of initiating immunological effector functions such as phagocytosis, antibody dependent cellular cytotoxicity (ADCC), degranulation, release of inflammatory mediators, production of oxygen radicals and regulation of antibody production. Soluble Fc gamma R in plasma play a modulator role in the immune system. The Fc gamma R expressed on endothelial cells (Brambell receptor: FcRB) is involved in regulation of IgG levels in blood and transport of maternal IgG to the unborn child. Experimental immunotherapy directed against haematological and solid tumours exploiting Fc gamma R-mediated functions has shown promising results.