Using energy-dispersive x-ray analysis (EDXA) in conjunction with a scanning electron microscope, high levels of sulfur were recorded in proboscis hooks of 5 species of Acanthocephala: Neoechinorhynchus qatarensis Amin, Saoud, and Alkuwari, 2002; Acanthocephalus dirus (Van cleave, 1931); Neoechinorhynchus idahoensis Amin and Heckmann, 1992, Echinorhynchus salmonis (Müller, 1784); and Pseudoacanthocephalus sp. Petrochenko, 1956. Sulfur was also present in eggs of N. qatarensis. No sulfur was recorded in the body of worms. The 5 species of Acanthocephala were obtained from several fish hosts and 1 toad species from 7 geographical locations. Sulfur ions are probably present in disulphide bonds characteristic of 2 amino acids, cystine and cysteine, which are common amino acids in the protein of mammalian hair and horns and are probably associated with the hardness of acanthocephalan proboscis hooks and egg shells.