Immunolocalization of CatB3 in metacercariae, NEJ, 4-week-old juvenile and adult F. gigantica performed by immunoperoxidase technique by using these MoAbs as probes indicated that CatB3 was present in high concentration in the caecal epithelium and caecal lumen of the Met and NEJ, but not in the 4-week-old juvenile and adult fluke.