A xanthan sample with molecular weight M=2.2x10⁶ was investigated in three solvents: bidistilled water, 0.2 M aqueous NaCl and cadoxen by flow birefringence and viscometry methods in dilute solutions. It was shown that the optical shear rate coefficients of xanthan in aqueous and cadoxen media differ by two orders of magnitude. An estimation of xanthan optical anisotropy in different conformational states has been made and compared with values for other polysaccharides: dextran, pullulan, cellulose and chitosan. The process of denaturation and the flow birefringence of renaturated xanthan in aqueous solutions (after heat treatment at 121°C) have also been studied. Copyright (C) 1999 Elsevier Science B.V.