Electron microscopic studies confirm and extend the conclusions derived previously from a quantitative biochemical study of the phagocytosis of polystyrene and polyvinyltoluene latex beads by Acanthamoeba (1). Latex beads 1.305, 1.90, and 2.68 micro in diameter are ingested individually, with each bead tightly surrounded by a membrane derived from the plasma membrane. Latex beads 0.557, 0.264, 0.126, and 0.088 micro in diameter are accumulated at the surface of the ameba and then phagocytosed, with many beads tightly packed within one membrane-bounded vesicle.