The shear history dependence of the viscosity of a depletion flocculated dispersion of colloidal spheres was studied using two different rheometrical geometries. The observed rheological behavior is found to depend on the geometry, due to effects of thixotropy and sedimentation. By comparing the results of a cone-plate and a Couette geometry, we were able to obtain reliable data. The shear history dependence is explored by measuring a flow curve before and after subjecting the aggregated dispersion to a constant shear rate for one hour. : The viscosity values of the flow curve after this hour turned out to be considerably lower than the initial flow curve. The results were interpreted with a microrheological model for fractal aggregation in shear flow. The drop in viscosity is attributed to a shear induced compaction of the aggregates. Combination of this model and the concept of compaction results in a satisfactory description of the experimental results.