The antibody-binding sites of the muscle larva of Trichinella spiralis were investigated by immunogold staining on the ultrathin sections of LR white resin. The antibodies, which were produced in the course of T. spiralis infection in rats, specifically bound to the inner layers of the body cuticle and the cuticle of the hindgut, but not to the cuticle of the esophagus. This is the first report that reveals the antigenic nature of the inner layers of the external coverings of T. spiralis larva.