This paper describes the fine structure of the sporogonic development of Plasmodium falciparum in its natural vector Anopheles gambiae (Species A) as seen by scanning and transmission electron microscopy. The parasite was derived from naturally infected volunteers and the vector maintained under natural conditions at the MRC Laboratories, Fajara, The Gambia. Sporogonic development of P. falciparum is similar to that described for other Plasmodium spp. There are however greater similarities between P. falciparum and the avian malaria parasites, than those mammalian (primarily rodent) species described to date--particularly with respect to mitochondrial development, crystalloid morphology and nucleolar organization. Nuclear development is similar to that of the murine malaria parasites, but reconstruction of complete mitotic spindles from serial sections suggest the haploid genome of P. falciparum contains 14 chromosomes compared to eight to ten in the murine plasmodia. Sporoblast formation involves a unique process of cleft formation based on the expansion of the cisternal space of the endoplasmic reticulum. Sporozoite budding is almost exclusively confined to these inner membrane surfaces and results in a characteristic sporozoite distribution in the oocyst. High resolution scanning electron microscopy of free sporozoites provides the first surface view of the micropore of Plasmodium.