The distribution and morphology of the Golgi complex and endoplasmic reticulum of epimastigote forms of the protozoan Trypanosoma cruzi were analysed at the ultrastructural level, after post-fixation of the cells with osmium tetroxide/potassium iodide. Intense staining was found in these structures, as well as in the nuclear envelope, showing that these compartments present a reducing environment. Positive reaction also demonstrates that intense protein synthesis occurs in the parasites which were collected at the log phase of growth. A Cis Golgi network (CGN) and an endoplasmic reticulum cistern associated with it could be clearly demonstrated. Different Golgi complex patterns were seen, suggesting that this organelle has a dynamic structure. In most cells, only peripheral cisternae directed to the endoplasmic reticulum presented an electron-dense reaction product, possibly corresponding to the cis region of the Golgi complex. Some parasites were also incubated in the presence of brefeldin-A, a drug which disorganizes the Golgi complex of several eukaryotic cells. Our results showed that T. cruzi epimastigote forms are resistant to brefeldin-A treatment, suggesting that the targets of drug action are absent in these protozoa.