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In an assay for Plasmodium falciparum, parasite cultures of P. falciparum were incubated in RPMI 1640 medium with 5% Albumax (without hypoxanthine). A series of meliltoside dilutions were applied in microtitre plates and incubated for 48 h at 37 C in a reduced oxygen atmosphere. In another assay, Trypanosoma brucei rhodesiense STIB 900 strain (10(4) blood stream forms of T. b. rhodesiense STIB 900 in 50 uL) was incubated at 37 C under a 5% CO2 atmosphere for 72 h in a medium (50 uM) supplemented with 25 mM HEPES, 1 g/L additional glucose, 1% MEM nonessential amino acids (100x), 0.2 mM 2-mercaptoethanol, 1 mM Na-pyruvate and 15% heat inactivated horse serum with addition of serial drug dilutions of seven 3-fold dilution steps covering a range from 90 to 0.123 ug/mL. Finally, in an assay for Trypanosoma cruzi, L-6 cells were seeded in 96-well microtitre plates in 100 mL RPMI 1640 medium with 10% FBS and 2 mM L-glutamine for 24 h. After that, the medium was removed and replaced by 100 uL per well containing 5000 trypomastigote forms of T. cruzi Tulahuen strain C2C4 containing the b-galactosidase (Lac Z) gene. The medium was removed from the wells after 48 h, and replaced by 100 uL fresh medium with or without a serial drug dilution of seven 3-fold dilution steps covering a range from 90 to 0.123 ug/mL and incubated for another 96 h. The compound demonstrated antiprotozoal activity with IC50 values of 58.9, 58.0 and 48.7 ug/ml against T. b. rhodesiense, T. cruzi and P. falciparum, respectively.