Abstract
The fusion of hamster peritoneal macrophages by lectins [concanavalin A, phytohemagglutinin] is described. The conditions under which this occurs are very similar to those previously reported using glutaraldehyde-fixed red cells and anti-hamster macrophage serum. Under conditions in which macrophages are brought into contact before interiorization of surface-bound lectin, fusion results. In granulomas, binding of endocytozable material to more than 1 macrophage apparently results in giant cell formation by a mechanism of simultaneous interiorization.