The aim of the present study was to evaluate, under in vitro conditions, the activity of 20 plant extracts against newly excysted Fasciola hepatica metacercariae. The plants were selected on the basis of anthelmintic activity, traditional use, availability, solubility, and permanence in the liver. For the in vitro evaluation, 24-well Nunc-immunoplates containing RPMI-1640 culture medium bovine sera plus antibiotics were used. Extract concentrations of 500 and 50 mg/mL were placed in triplicate. Approximately 10 newly excysted flukes were placed in each well, and the plates were incubated in a CO(2) incubator at 5% atmosphere for 3 days. In each plate four control wells containing nontreated flukes were included. All procedures were undertaken under an air-flow cabinet. Efficacy was measured on days 1 and 3 by considering the motility of the live or dead trematodes evaluated with the aid of an inverted microscope. Results indicated that, from all extracts evaluated, Tilia mexicana showed an average efficacy for concentrations of 500 and 50 mg/mL, respectively, of 100 and 100%; Eriobotrya japonica, 100 and 95%; Coffea arabica, 100 and 100%; Crataegus mexicana, 95 and 90%; and Ternstroemia pringlei 100 and 100%. From this preliminary evaluation, we conclude that further and more detailed evaluations at lower concentrations should be undertaken to understand the real efficacy of these plant extracts.