Electron microscopy of erythrocytes infected by the malarial parasite, Plasmodium falciparum, revealed electron dense, cone-shaped excrescences (∼40 mμ in height and ∼100 mμ in width) along the plasma membrane. These excrescences form focal junctions with the plasma membrane of reticular cells of the spleen. The resulting complexes appear to be responsible for sequestration of erythrocytes infected by P. falciparum in the spleen of the host.