The motion of a particle of size 'a' due to an imposed external force through a suspension of colloidal particles is investigated analytically and numerically. The particle's translational velocity is determined by a balance between the imposed force and the reactive force of the colloidal dispersion, which consists of the viscous Stokes drag and a Brownian force caused by the microstructural deformation. The Peclet number (Pe = Fa/ kT), the ratio of the external force (F) to the Brownian force (kT/a), governs the distortion of the microstructure. At small Pe the response is viscous, with a linear relation between the imposed force and the particle velocity. As the Peclet number is increased the particle's velocity decreases with increasing Pe until a viscous plateau is reached at infinite Pe. This 'shear thinning' of the particle's velocity is reminiscent of the shear thinning of the dispersion's viscosity.