Steady and dynamic oscillatory rheometry were used to characterize two members of the plant polyphenols from Pinus radiata bark, water-soluble proanthocyanidin polymers, and phenolic acids. The viscosity-controlling factor of the extracts could be revealed by examining the various extracts under different chemical and theological environments. Water-extracted (100 degrees C) bark was successively extracted with aqueous NaOH solutions of increasing alkalinity at 100 degrees C and the theological characteristics of the each fraction were examined in detail. The significant viscoelasticity of the 100 degrees C aqueous NaOH sequential extracts suggests that this fraction can have a critical impact on the flow characteristics of overall extracts and arises from a major contribution of colloidal interactions involving the carbohydrate component.