In a previous paper Pinto and Ray (1995, Chem. Engng Sci. 50, 715-736) developed a mathematical model to describe the dynamic behavior of continuous free-radical solution copolymerization reactors and validated the model with experimental results obtained for the copolymerization of vinyl acetate (VA) and methyl methacrylate (MMA) in tert-butanol(TB). The model is now extended to allow the analysis of the dynamic effects induced by the presence of inhibitors in the reaction environment. It is shown both theoretically and experimentally that the existence of small amounts of inhibitors in the feed stream may lead to the development of unstable operation; in particular, oscillatory behavior and multiple steady-state conditions.