The temporal expression during gametogenesis and the cellular location of the sexual stage specific protein Pfs16, a putative integral membrane protein of Plasmodium falciparum, was investigated using two monoclonal antibodies, 2G7 and 93A3A2. Using sorbitol synchronised, in vitro gametocyte cultures along with immunofluorescence assays, the time at which Pfs16 is first expressed during gametogenesis has been estimated to 35 hours post merozoite invasion. By immunofluorescence assays on thin blood smears monoclonal antibodies specific for Pfs16 react strongly with the gametocyte and also with vesicles within the red blood cell cytoplasm, many of which connect with the gametocyte cell. Purification of parasitophorous vacuole membranes from mature and immature gametocytes and immunoelectron microscopy on gametocytes during gametogenesis have allowed us to locate Pfs16 to the parasitophorous vacuole membrane. During gametogenesis this membrane is shed along with the red blood cell membrane. Immunofluorescence assays and immunoelectron microscopy studies of emerged gametes indicate that in a minority of cases the parasitophorous vacuole membrane along with Pfs16 can be retained to some extent on the gamete surface.