Nine Rocky Mountain bighorn sheep (Ovis canadensis canadensis) were each inoculated orally with 250 metacercariae of Fasciola hepatica. Blood and fecal samples were collected at the time of inoculation and at 5, 10, 14, and 20 wk after inoculation. Numbers of fluke eggs in feces, hemoglobin, packed cell volume, and eosinophil values were determined. Five of the bighorn sheep were treated with triclabendazole at 40 mg/kg of body weight 14 wk after inoculation. Based on fecal evaluations, all bighorns developed patent infections. Six weeks after treatment, fluke eggs were not detected in feces from the five treated animals but were present in two of four untreated animals. One untreated bighorn sheep was euthanized 20 wk after inoculation, and 57 adult F. hepatica were recovered from the liver. Results from this experiment indicated that bighorn sheep are efficient hosts for F. hepatica. Triclabendazole at 40 mg/kg of body weight was safe and, based on fluke egg recovery in feces, apparently an effective treatment. To my knowledge, this is the first published report of F. hepatica in bighorn sheep.