Copper(II) or nickel(II) complex formation with an insolubilized cross-linked poly(acrylic acid) was investigated in dilute aqueous solution (0.1 mol l −1 NaNO 3; 25°C). Potentiometric titrations were carried out, first to precisely measure the acid–base properties of the polymer, and secondly to determine the stability constants of the MA and MA 2 complex species formed. Bjerrum’s method, modified by Gregor et al. (1955) for the study of polymeric acids was used. The results obtained showed that copper(II) was more readily bound to the polymer than nickel(II). For the operative conditions considered here, CuA 2 was the predominant observed species; the global stability constant log β 102 was found to be 6.6. With nickel(II), neither of the complex species MA or MA 2 becomes predominant (log β 102 = 5.4). Finally, the results were compared to those obtained previously under the same conditions with two hydrosoluble poly(acrylic acids) (HPAAs) of high molecular weight; it appeared that linear and cross-linked polymers present identical binding properties.