The activity of jatrogrossidione, the main diterpene of Jatropha grossidentata and jatrophone from Jatropha Isabella was determined against Leishmania and Trypanosoma cruzi strains in vitro as well as against Leishmania amazonensis in vivo. Jatrogrossidione showed a strong in vitro leishmanicidal and trypanocidal activity with IC100, of 0.75 and 1.5-5.0 μg/mL, respectively. Under similar conditions, the IC100 of glucantime, ketoconazole and pentamidine towards Leishmania strains were >100, 50-100 and 1 μg/mL, respectively. The IC50 of jatrogrossidione was <0.25 μg/mL against amastigote forms of Leishmania infecting macrophages, with toxicity at concentrations higher than 0.5 μg/mL. BALB/c mice infected with L. amazonensis strain PH 8 were treated 24 h after infection with jatrogrossidione and jatrophone for 13 consecutive days. Jatrophone at 25 mg/kg/day subcutaneously administered was significantly active (p<0.05) against the virulent strain PH 8 of L. amazonesis; it was more active than Glucantime at 112 mg Sbv per kg/day. Subcutaneous administration of jatrophone, however, proved to be too toxic under our assay conditions. Assays of single local treatment on the footpad infection 2 weeks after inoculation of L. amazonensis indicated that jatrogrossidione and jatrophone were inactive at the selected doses. © 1996 by John Wiley & Sons, Ltd.