Actin is associated with intraerythrocytic transport vesicles. Trophozoite stage IRBCs were treated with AlF and processed for immunoelectron microscopy using an antiactin antibody. Actin associated with the RBC membrane and (A-B) coated vesicles in the RBC cytosol, (C) vesicle chains in the RBC cytosol closely apposed to the RBC membrane, and (D-E) vesicles (arrowhead) with a translucent limiting membrane and electron dense contents closely apposed to the RBC membrane. (F) Actin in close proximity to a coated vesicle budding from the PVM, black arrowhead, (G) concentrated in protruding areas of the PVM, black arrowhead, (H) associated with the Maurer clefts, which appeared to extend to actin-rich areas (black arrowheads) and a protruding, electron-dense area of the PVM (short arrow) that was similar in appearance (translucent limiting membrane and electron-dense contents) to the vesicles in panels D and E. (I) Maurer clefts in IRBCs permeabilized with streptolysin O maintained their parallel orientation and appeared to be tethered to the RBCs and parasite membranes via actin. Scale bar = 70 nm.