The authors report on the viscoelastic characterization of guar hydrogels obtained through complexation reactions with borax ions. These gels are compared with hydrogels obtained from poly(vinyl alcohol) of different degree of hydrolysis through complexation reactions with congo red. The effect of the degree of hydrolysis and both the concentration of PVA and the concentration of congo red, on the viscoelastic properties of the hydrogels is analyzed. The potential use of the PVA-based hydrogels as hydraulic fracturing liquids is discussed in relation to the commonly used fracturing liquid based on the guar-borox system. (C) 2008 Wiley Periodicals, Inc. J. Appl Polym Sci 110:695-700, 2008