We produce concentrated (40 vol%) gels of uniformly sized silica particles by an in situ process, based on the enzyme-catalyzed hydrolysisof urea in the liquid phase of electrostatically stabilized suspensions. Two different methods are used: Either the pH of the suspensions isshifted toward the isoelectric point of the particles (??pH method), or the ionic strength is continuously increased at constant pH (??I method).We compare the two kinds of gels in terms of elastic and yield behavior as well as microstructure by using rheological measurements inoscillation and high-pressure freezing in combination with cryo-SEM, respectively. Results suggest a strong increase of elastic and yieldproperties in concentrated particle gels with decreasing homogeneity of their microstructures.