In the present study different dye-to-protein ratios were used for the conjugation of rabbit anti-gonococcal globulin with fluorescein isothiocyanate. The conjugates were fractionated on DEAE-cellulose columns. The fractions obtained were tested for specific and nonspecific reactions by FAT; they were also examined by immunoelectrophoretic analyses and in the gonococcal complement-fixation test. Specific antibody activity was correlated with the presence of γG-globulin molecules; the non-specific staining of leucocytes in FAT was found exclusively in fractions containing heavily-labelled γG-globulin molecules. Even when these molecules were removed by chromatography on DEAE-cellulose, a satisfactory, specific staining of gonococci in direct smears of secretion was not obtained.