The quantity of anti-IgG bound at equilibrium to cell-bound anti-D failed to increase with enzymatic modification of intact red blood cells. This contrasts with results obtained by immunoelectronmicroscopy with unsealed red blood cell ghosts. Ghosts derived from enzyme-modified, anti-D-sensitized intact red blood cells show an increased ratio of anti-IgG to anti-D. The ratio declined with protease modification of intact cells, possibly because of steric hinderance to anti-IgG binding within the cellular agglutinates. At comparable levels of cell-bound anti-D and anti-IgG, enzyme-modified cells were more agglutinable in the antiglobulin reaction than unmodified cells. As in saline hemagglutination, enzymatic enhancement of agglutinability appears to be unrelated to the amount of antibody bound, but rather may be related to other factors such as alterations of the biophysical properties of the red blood cell membrane.