Sheep experimentally infected with Fascioloides magna were used in a controlled study to determine the flukicide activity of different doses of albendazole (methyl [5(propylthio)-1H-benzimidazol-2-yl] carbamate). Sheep, about 4 months old, were inoculated with 100 metacercariae of F magna and treated with the various doses of albendazole 10 weeks later. At 6 weeks after treatment, the sheep were necropsied, flukes were recovered and measured, and the pathologic changes were recorded. The sheep were given different doses of albendazole (5, 7.5 [single dose or double dose], 10, and 15 mg/kg) and were compared with both nontreated inoculated and nontreated noninoculated controls. There were up to 70% fewer worms recovered in the group given 2 doses of 7.5 mg/kg than there were in the nontreated controls. There was also a significant reduction in flukes recovered in the groups given the 7.5, 10, and 15 mg/kg doses. Because a single F magna fluke has the potential to kill a sheep, it is imperative to consider the number of sheep with no flukes after treatment. According to that criterion, 50% of the sheep were protected at dose rates of 7.5 (single dose, double dose), 10, and 15 mg/kg of body weight.