The aggregation of concentrated aqueous silica suspensions is characterized by means of static light scattering. We use an in situ destabilizationmechanism based on the enzyme-catalyzed hydrolysis of urea. This method enables us to continuously and homogeneously changethe interparticle potential from repulsive to attractive without disturbing the aggregation process. Moreover, our electrostatically stabilizedsuspensions can be destabilized by two different methods. In the first method, the pH is shifted toward the isoelectric point of the particles(??pH method), thereby leading to a decrease of their surface charge. In the second method, the ionic strength is continuously increased atconstant pH (??I method), leading to a compression of the electrical double layer around the charged particles. A laboratory-built flat-celllight-scattering instrument is used, which allows fast data acquisition and an adjustment of the sample cell thickness. To circumvent multiplescattering effects, we use a very small sample thickness (Å13 μm). In addition, the refractive index difference between the aqueous phaseand the particles is reduced by adding sucrose to the liquid phase of our suspensions. We are able to characterize the structural changes atthe very early stages of the destabilization process, where no significant effects are yet detected in macroscopic rheological measurements.While during the ??pH destabilization, the scattering curve shows significant changes only after some characteristic delay time, it changes continuously during the ??I destabilization. The latter is attributed to the formation of a weak pre-gel structure in the suspensions, as a shallow secondary minimum appears in the interparticle potential. Data are evaluated by using a HMSA square-well structure factor model.Results are in good agreement with those predicted from DLVO theory.