We have applied several immunolabeling techniques using a monoclonal antibody to a Plasmodium falciparum antigen to differentiate morphologically dissimilar membranous structures present in infected erythrocytes. Evidence is presented that cytoplasmic clefts, multimembranous structures and vesicles within the infected cell originate from the parasitophorous vacuole membrane by a process described as budding off. The parasitophorous vacuole membrane and related structures in infected, parasitized erythrocytes reacted with the cyanine dye Merocyanine 540, demonstrating that they are accessible to molecules from the extracellular environment. Immunogold labeling of freeze-fractured preparations and of thin sections of parasitized cells using pre- and post-embedding techniques revealed that each of the membranous structures carried a common parasite antigen, QF 116, which was identified by monoclonal antibody 8E7/55.