The effect of Allium sativum (Liliacea) on trypanosome-infected mice was examined. At a dose of 5.0 mg/ml, the oily extract from the pulp completely suppressed the ability of the parasites to be infective in the host. Column chromatography of the extract gave four fractions: ethylacetate/methanol, ethylacetate/ethanol, benzene/methanol, and acetic acid/methanol. Among these fractions, the acetic acid/methanol fraction retained the trypanocidal features of the crude extract. It cured experimentally infected mice of trypanosomiasis in 4 days when given at a dose of 120 mg/kg per day. The extract also manifested inhibition of procyclic forms of Trypanosoma brucei brucei and phospholipases from T. congolense, T. b. brucei, T. vivax. The extract appears to be diallyl-disulfide (DAD) and may interfere with the parasites' synthesis of membrane lipids.