The ground dried rhizome of the plant, Curcuma longa LINN has long been used as a naturally occurring medicine for the treatment of inflammatory and other diseases, and has also been used as a coloring agent and spice in many foods. 1)The powdered rhizome is commonly called turmeric. Curcumin (diferuloylmethane) is a major active ingredient that has been identified as the major pigment in turmeric. Curcumin is well known as a potent anti-oxidant, 2,3) and recent studies have revealed that it is a potent inhibitor of reactive oxygen-generating enzymes, such as lipoxygenase/cyclooxygenase, 4,5) xanthine dehydrogenase/oxidase 6) and inducible nitric oxide synthase 7) and it possesses anti-inflammatory activity. 8,9) Moreover, it has shown anti-carcinogenic activity in animal models, such as colon tumor initiation by azoxymethane 10) and skin tumor promotion induced by phorbol ester TPA.11) Recently, curcumin has been considered by oncologists as a potential third generation cancer chemopreventive agent, and clinical trials using it have been carried out in several laboratories.Leishmania such as Leishmania major are the protozoan parasite responsible for leishmaniasis. So far, medicines used for the treatment of leishmaniasis such as pentavalent antimonials and pentamidine are toxic or have severe side effects, for example renal, cardiac and neural toxicity, shock and risk of diabetes.12) Other medicines such as amphotericin B are restricted to hospital use. In addition, resistance towards these medicines have been observed. 13) Thus, the development of a new agent is urgently needed.During the search for the candidate of anti-parasitic agents from natural resources, we have found that curcumin has leishmanicidal activity in vitro. MATERIALS AND METHODSChemicals Curcumin was purchased from Funakoshi Co., Ltd. (Tokyo, Japan) and other chemicals used were special grade.Axenic Cultivation of Leishmania The medium used for the cultivation of promastigotes of L. major (MHOM/ SU/73/5ASKH) was SDM-79, previously described by Brun and Schonenberger.14) Leishmania were cultured into 25 cm 2 -tissue culture flasks containing 5 ml of culture medium per flask and maintained therein at 27°C in an atmosphere of 5% CO 2 -95% air.Leishmanicidal Assay Cultured leishmania of promastigotes were centrifuged at 600 g for 5 min at 4°C, and the parasites then resuspended with culture medium, diluted to a density of 5ϫ10 5 /ml and inoculated into 96-well plate. The medium (0.1 ml) containing various concentrations of curcumin dissolved in dimethyl sulfoxide (DMSO) was added into each well and incubated at 27°C in an atmosphere of 5% CO 2 -95% air. The final concentration of DMSO was 0.5%. After incubation for an appropriate period, the number of surviving leishmania was determined microscopically by counting in a Burker-Turk hemocytometer. The leishmanicidal activity of curcumin was shown as 50% growth inhibitory concentration (GI 50 ), 100% growth inhibitory concentration (TGI) and LD 50 after incubation with leishmania for 24 h. 100% gr...