An electron microscopy study was carried out on the salivary glands of the triatomine bug Rhodnius ecuadoriensis experimentally infected with a Peruvian strain of Trypanosoma (Herpetosoma) rangeli. Epimastigotes forms of T. rangeli were found in large numbers in the haemolymph surrounding the salivary gland. Some of them were closely associated with the basal lamina of the gland epithelium, apparently in a process of cell invasion, in which the flagellum breaking through the basal lamina. Within the cytoplasm of the gland epithelial cells, there were rounded forms of T. rangeli, consisting of tightly coiled sphaeromastigotes. The gland lumen was filled with large numbers of mostly epimastigotes forms of the flagellate; only few paramastigotes and trypomastigotes forms could be unequivocally identified. The presence of paramastigotes in the life cycle of T. rangeli has yet to be fully assessed