Two groups of mice, showing a patent infection of Schistosoma mansoni, were orally treated with an alcoholic extract of Ambrosia maritima leaves. One group received a single dose, equivalent to 15 g leaves/kg body weight, whereas the other received 5 consecutive doses. The schistosomicidal activity of the plant extract was evaluated 1 week after treatment using 4 parameters: worm load, motility of the worms, oogram and the number of eggs in the liver and intestinal wall. In comparison to the control group no effect at all was observed in the mice who received one single dose of A. maritima. In the group receiving 5 consecutive daily doses, however, the percentage of immature eggs in the intestinal wall had slightly decreased as compared to the controls, but this was compensated by an increase in the number of eggs in the liver. Given the high doses of plant extract used, it is concluded that oral administration of A. maritima has a negligible effect on S. mansoni in mice.