Erythrocytes infected with Plasmodium vivax show unique ultrastructural changes which include membranous structures in the host cell cytosol, called clefts, and caveola-vesicle complexes (CVC) in the infected erythrocyte membrane. It has been suggested that the latter structures correspond with the Schuffner's dots observed on Giemsastained thin films. The subcellular localization of a 28 kDa and a 95 kDa antigen of the erythrocytic stages of P. vivax was determined by post-embedding immunoelectron microscopy. Four monoclonal antibodies (MAbs) (2H12.B4, 2H8.E10, 1H4.B6, and 4C12.G4) against the 95 kDa protein reacted with the vesicles of CVC and vesicles scattered in the cytoplasm of the infected erythrocytes. Two other MAbs (4C12.B10 and 4D7.B1) against a 28 kDa protein reacted with the cytoplasmic clefts and were also reactive with the vesicles and electron dense materials in parasitophorous vacuole. These parasite-induced structures make a contribution to the movement of some malaria proteins from the parasite to the erythrocyte surface.