Lysozyme interactions in an aqueous solution are modeled via the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. We calculate the structural functions at different pH values by means of Monte Carlo computer simulation and integral equation theories. The theoretical structure factor is then used to evaluate the scattered intensities, which are compared with the experimental small-angle neutron scattering data reported in Philos. Mag. 2011, 91, 2066. We find that the DLVO theory reproduces only qualitatively the tendency of protein interactions to become more short-range and attractive at low ionic strength; however, at sufficiently high ionic strength, the theory becomes quantitative. At the higher investigated pH values, DLVO theory predicts the formation of protein aggregates driven by the competition of short-range attraction and long-range repulsion.