Epimastigotes and trypomastigotes of Trypanosoma cruzi were observed by scanning electron microscopy. These two forms could easily be differentiated by examination of the undulating membrane and kinetoplast. Subpellicular microtubules form parallel helices in epimastigotes while they are arranged parallel to the logitudinal axis in trypomastigotes. Some epimastigotes and trypomastigotes showed a "knob-like" swelling at the end of their bodies.