Amastigotes of L. donovani strain MHOM/ET/67/L82 were grown in axenic culture at 37 °C in SM medium at pH 5.4 supplemented with 10% heat-inactivated fetal bovine serum under an atmosphere of 5% CO 2 in air. One hundred microlitres of culture medium with 105 amastigotes from axenic culture with or without a serial drug dilution were seeded in 96-well microtiter plates. Serial drug dilutions of eleven 3-fold dilution steps covering a range from 100 to 0.002 μg/ml were prepared. After 70 h of incubation, the plates were inspected under an inverted microscope to assure growth of the controls and sterile conditions. 10 μl of resazurin (12.5 mg resazurin dissolved in 100 ml distilled water) were then added to each well and the plates incubated for another 2 h.