The effect of acid-base equilibria on the properties of polyelectrolyte solutions is investigated using the self-consistent polymer reference interaction site model theory with the random phase approximation. In the model, each monomer on the chain consists of charged and protonated sites, which contribute an electrostatic repulsion and a short-ranged attraction, respectively. The proportions of charged and protonated sites are governed by a chemical equilibrium constant. The polymer chains are highly charged and expanded when the strength of attraction is low. As the strength of the attraction is increased, the monomer fractional charge and chain size decrease in a continuous or discontinuous manner, depending on the equilibrium constant. For a fixed value of the strength of the attractive interaction, the monomer charge fraction and chain size display a nonmonotonic dependence on the concentration. The theory could provide a rationalization of some recent experimental measurements of the conformational and structural properties of DNA fragments and synthetic polyelectrolytes. (C) 2001 American Institute of Physics.