Our study concerns the expression and the regulation of adhesion and activation receptors on human NK cells. In particular we provide evidence on: a) the expression on fresh human NK cells of VLA-4, VLA-5 and VLA-6, extracellular matrix (ECM) receptors of integrin family capable of mediating their adhesion to FN and LM; b) the role of PKC on the regulation of CD16, a differentiation antigen associated with FcγR type III expressed by all NK cells, which mediate ADCC activity and trigger lymphokine production.