Short-range attraction and long-range electrostatic repulsion among the lysozyme proteins in solution have been identified which are modified depending upon the protein concentration, solution pD, dissolved ions and solution temperature. Small angle neutron scattering study shows that for a particular pD, with increasing protein concentration, attractive interaction increases but repulsive interaction first increases and then decreases. With increasing solution pD, attractive interaction increases and repulsive interaction decreases, however this trend is not valid for very low and high protein concentrations. Presence of monovalent salt largely enhances the attractive interaction however the enhancement is low for the heat treated lysozyme solution. (c) 2015 Elsevier By. All rights reserved.