The synthesis and swelling behavior of a new superabsorbent hydrogel based on natural salep grafted with polyacrylamide is described. The new biopolymer was synthesized via simultaneous crosslinking and graft copolymerization of acrylamide monomer onto a salep backbone using radiochemical methods. Various parameters Such as relative contents of salep, and acrylamide. as well as total dose of gamma-rays were examined. The best synthesis condition is reported and a mechanism for superabsorbent hydrogen formation suggested. Factors affecting the swelling behavior of hydrogel were also Studied. (c) 2008 Elsevier B.V. All rights reserved,