The theory of the "neighbor effect" was applied for the description of the potentiometric titration curves of polyelectrolytes. Satisfactory results for poly(acrylic acid) were obtained by considering the effect of the two (at the right and at the left) nearest neighbors on the state of the monomeric unit in the limits of triads. The developed method was used for the determination of the degree of linkage of acidic groups in solutions of the interpolymer complexes.