Seven lignans isolated from the hexane extract of the leaves of Zanthoxyllum naranjillo (Rutaceae) were tested in both in vitro and in vivo assays against two strains of Trypanosoma cruzi (Bolivia and Y). Of the seven assayed lignans, three were inactive [(+)-sesamin, (+)-piperitol-4'-O-gamma, gamma-dimethylallyl ether and (-)-3,4-dimethoxy-3',4'-demethylenedioxycubebin] and three were partially active in the in vitro assays [(-)-hibalactone, (-)-kaerophylin and (-)-cubebin]. Healthy animals developed the disease after injection of the tested infected blood samples containing these three compounds. One compound [(-)-methylpluviatolide] was highly effective in the in vitro assay and healthy animals injected with the tested samples did not develop the disease. Moreover, only (-)-methylpluviatolide was highly active against the bloodstream forms of both strains of T. cruzi for the in vivo assay. However, it was not active against the tissue forms of the parasite.