Summary. We assessed the biological activity of a plant powder, crude extracts, and several fractions obtained from Tanacetum parthenium on Leishmania amazonensis. The medicinal plant T. parthenium is indicated for prevention of migraine headache crises, and several investigations have already demonstrated its anti-inflammatory activity. This study included the extraction process and bioassay-guided fractionation by the adsorption chromatography method. A progressive increase in the antileishmanial effect was observed in the course of the purification process. The plant powder (PTP) had a 50% inhibitory concentration (IC 50 ) at 490 µg/ml, whereas the dichloromethane fraction (DF) showed an IC 50 of 3.6 µg/ml against the growth of promastigote forms after 48 h of culturing. In axenic amastigote forms, the IC 50 of the PTP and DF were 74.8 µg/ml and 2.7 µg/ml, respectively. Cytotoxicity analysis indicated that the toxic concentrations of the PTP, ethyl-acetate crude extract (ECE), and DF were much higher for J774G8 macrophages than for the protozoans. Haemolytic experiments were performed, and the ECE and DF did not cause lysis at concentrations higher than the IC 50 for promastigotes
