FcgammaRIII(CD16), one of the low-affinity IgG Fc receptors exists in two forms. FcgammaRIIIa is expressed on NK cells, a subset of T lymphocytes, a subpopulation of monocytes and macrophages, and shows a cell type specific glycosylation pattern. FcgammaRIIIb is expressed exclusively on neutrophils in two allotypes, NA1/2, and it can be induced on eosinophils. Both FcyRIIIs are released from the cell surface. FcgammaRIIIa is released by the action of a metalloprotease upon the in vitro activation of NK cells and macrophages. FcgammaRIIIb is released upon activation and during the apoptosis of neutrophils by proteolytic activity. So, the amount of each type of soluble FcgammaRIII means the activation of each type of cell. We measured three types of soluble FcgammaRIII in plasma and also urine with newly developed anti-FcgammaRIIIa and anti-FcgammaRIIIa(Mphi) monoclonal antibodies. We found that sFcgammaRIIIa may be a novel marker of inflammatory activity in rheumatoid arthritis. sFcgammaRIIIa(M phi) may serve as predictive marker for atherosclerosis. Further, urinary sFcgammaRIIIa and sFcgammaRIIIa(Mphi) may be novel markers for the assessment of disease activity in nephritis.