Enzyme-linked immunosorbent assay was used for determination of the concentration of soluble Fc gamma receptor III (Fc gamma RIII) in 40 samples of gingival fluid obtained from periodontal pockets in 30 patients with periodontitis. The assay was based on a monoclonal immobilized antibody binding Fc gamma RIII and a polyclonal Fc gamma RIII rabbit antibody for its quantification. The results indicate a substantially increased concentration of soluble Fc gamma RIII in gingival fluid as compared to the serum level. This increased concentration of soluble Fc gamma RIII may interfere with phagocytosis and immune homeostasis in the periodontal lesions.