Soluble Fc gamma receptors are produced by cleavage of the membrane receptors or by alternative splicing. They are found in biologic fluids. After a brief description of the structure and mode of production of soluble Fc gamma R, we address the question of ligands and function of the soluble Fc gamma R by using recombinant molecules and transgenic animals. We show that soluble Fc gamma R are not only IgG-binding factors which interfere with, and block, Fc-dependent immune reactions but also molecules that interact, in vitro, with non-Ig-ligands such as CR3 and CR4 and are trigger or regulate immune functions via these receptors.