Freeze-fracturing has been used to study the ultrastructure of the sporozoites of the malarial parasite Plasmodium vivax within the salivary gland of the mosquito Anopheles stephensi. The architecture of the pellicular complex of the salivary gland sporozoites was essentially the same as that reported for the intraoocystic forms, but the outline of cross-fractured P. vivax sporozoites was more flattened and crescent shaped as opposed to the circular outline described for the intraoocystic sporozoites. The salivary gland sporozoites of P. vivax also exhibited apical rosettes and a cytosome connected to a food vacuole, two unique structures not previously reported for malarial sporozoites.