From the beginning of this decade and with the revival of the phytotherapy, biological research about immunomodulatory, anti-inflammatory and antiprotozoal effects of Central and South American plants have been in progress. Our objective was to determine the antiprotozoal activity of 79 extracts from different plant families, including Asteraceae, Araceae, Moraceae, Solanaceae, Rhamnaceae, Zingiberaceae, Leguminosae and Sapotaceae. Once matching with herbarium specimens authenticated the plants, selected parts were separated, dried carefully and reduced to powder. Most of the screened extracts were aqueous. Two protozoa with different metabolic pathways, Trypanosoma cruzi and Trichomonas vaginalis were used as experimental models. Trypanocidal activity of plants was assayed on epimastigote cultures in liver infusion tryptose (LIT). Anti-Trichomonas activity was determined over cultures of the parasite in Diamond medium. In both cases, microscopic counting of parasites, after their incubation in the presence of different concentrations of the crude extracts, were made in order to determine the cytocidal and cytostatic activities respect to control cultures. Of the nine extracts that showed antiprotozoal activity, those from Mikania cordifolia and Philodendron bipinnatifidum were then fractionated, and again, were assayed the organic and aqueous phases obtained.