In order to observe the antigenic localization in the tissues of Paragonimus westermani of developmental stages, immunogold labeling method was applied using serum of the cats which were infected with isolated metacercariae from Cambaroides similis. The sectioned worm tissues from each developmental stage were embedded in Lowicryl HM 20 medium, stained with infected serum IgG and protein A gold complex (particle size: 12 nm) and observed by electron microscopy. In the young adult worm tissue of 4 weeks after infection with metacercariae, the gold particles were specifically concentrated on the tegumental syncytium and cytoplasm of the tegumental cells as well as the secretory granules in the parenchymal tissue. The antigenic materials in the adult worm tissue were specifically concentrated on the secretory granules in the parenchymal tissue, the cytoplasm between granules in the vitelline gland and the epithelial lamella in the lumen of the caecum.
