Viscosity and oscillatory shear measurements have been performed on kappa-carrageenan alone and on kappa-carrageenan/galactomannan (guar gum or locust bean gum) blends in the vicinity of the sol-gel transition. From these measurements, a phase diagram showing the boundary limits for kappa-carrageenan/locust bean gum and kappa-carrageenan/guar gum was established. The viscoelastic behaviour at the transition showed that this process was sharp for the kappa-carrageenan/locust bean gum blend, while for the kappa-carrageenan/guar gum blend, it was more progressive. The kappa-carrageenan content at which the transition took place was estimated and was found to be constant, whatever the total polymer concentration of the mixture studied. This phase transition results in a system whose theological properties are far removed from those of the original biopolymers. However, it is shown that kappa-carrageenan is primarily responsible for gel network formation.