AbstractGuinea pig peritoneal macrophages have on their surface two receptors, one (Fcγ1/γ2R) binding both guinea pig IgG1 and IgG2 and the second (Fcγ2R) binding only IgG2 immunoglobulins. We have previously shown that treatment of macrophages with neuraminidase or glycosylation inhibitors affects, in a different way, the binding of guinea pig IgG1, IgG2, and rabbit IgG. In the present study we have shown that pretreatment of guinea pig macrophages with lectins (Con A, WGA, and PNA) also has a different effect on the interaction of the cells with IgG. The lectins increased the binding of guinea pig IgG1, whereas rabbit IgG and guinea pig IgG2 were bound with a lower efficiency than in the case of control cells. Since sialic acid residues seem to modulate the activity of receptors and WGA interacts with sialylated oligosaccharides, we determined the IgG‐binding characteristics for WGA‐pretreated macrophages. We found that the increase in IgG1‐binding ability was caused by an increase in the value ofKapp, but the number of IgG‐binding sites was lower than in the control cells. In the case of rabbit IgG and guinea pig IgG2 we observed a decrease of both the value ofKappand the number of IgG‐binding sites. WGA did not interact directly with the Fcγ receptor. The results of our former papers and the different effects of lectins of various specificities described in this paper suggest different positions of Fcγ1/γ2and Fcγ2R in the plane of the plane of the macrophage membrane in respect to various membrane glycoconjugates. Interaction of IgG with macrophage Fcγ receptors depends in a different way on glycoconjugates on the surface of the macrophage. Our results suggest that changes in glycosylation of macrophage surface glycoconjugates may be used by the cell for regulating the binding activities of the macroph