The viscosimetric behaviour and the preferential solvation of poly(methacry1ic acid), (PMA, poly(1-carboxy-1-methylethylene)) and poly(2-hydroxyethyl methacrylate), (PHEMA, poly[l-(2-hydroxyethoxycarbonyl)-1 -methylethylenel) in water/2-~hloroethanol mixtures were studied. The system PHEMA/water/2chloroethanol is a typical polymer/solvent/precipitant system in which 2-chloroethanol is preferentially solvated in the whole range of solubility. On the contrary, the system PMA/water/2-chloroethanol is a typical cosolvent system which exhibits the so-called inverse adsorption. This difference is attributed to the more hydrophilic character of the carbonyl group in PMA.