Cutaneous and mucocutaneous leishmaniasis are endemic diseases in South America, especially in the subandean areas of the humid lowlands of Bolivia. Fourteen plants used topically in folk medicine to treat cutaneous leishmaniasis were collected in the tropical regions of colonization and in the rain forest occupied by Chimane Indians. Three of four plants used by the Chimane Indians exhibited an in vitro activity against three species of Leishmania. Two of ten plants used by the colonists showed an in vitro activity. We have also included results obtained with extracts from 53 Bolivian medicinal plants used for other diseases and from 43 plants collected with basis of chemotaxonomic criteria from all parts of Bolivia. All extracts were also screened in vitro against three strains of Trypanosoma cruzi (Trypanosomatidae), the causative agent of Chagas' disease.