In this paper we present some preliminary Small Angle Neutron Scattering results about the influence of pH and temperature on the structure of macromolecular solutions. We have investigated aqueous solutions of lysozyme at concentrations of 0.05, 0.10 and 0.15 w/w, at pH values of about 3, 5, and 6.7, and in the temperature range of 10-50-degrees-C. At the lower values of the pH, well defined interaction peaks are present in the scattered intensities, whereas at the higher pH an unstructured aggregation takes place, which is reduced by the increase in temperature.