Copolymers sensitive to pH intended for site-specific drug delivery, in particular for colonie delivery, were synthetised by reaction in a fixed molar ratio (70/30) of the nonionic hydrophobic moieties vinyl acetate, methyl acrylate, methyl methacrylate, ethyl acrylate or ethyl methacrylate with acrylic acid or methacrylic acid, in the presence of ethylene glycol dimethacrylate as a crosslinking agent. Equilibrium and dynamic swelling experiments were performed in solutions of pH ranging from 1.2 to 7.0. Most promising results were obtained with poly(methyl acrylate-co-methacrylic acid) and poly(ethyl acrylate-co-methacrylic acid), which were thus selected to study the effect of the monomeric ratio (90/10 to 30/70) and that of the crosslinking ratio (0.15, 0.30 or 0.45 mol %). Swelling was totally absent in acidic media and occurred only above pH 6, but its extent could be modulated by either of the two aforementioned factors. lnterestingly, the mechanism of water penetration was relaxation-controlled (case II transport).