We investigate the nonlinear theological behavior of colloidal suspensions of Laponite, a synthetic clay, driven by steady homogeneous shear strain. We show that the external drive leads to drastic slowing down of the aging dynamics or even, in some cases, in rejuvenation of the system. Under shear, after a surprisingly long time, the spontaneous aging process observed at rest is suppressed. The system then reaches a nonequilibrium stationary state that is characterized by complex viscosity depending on the shear rate applied. In addition, the glass exhibits non-Newtonian shear-thinning behavior. This theological behavior confirms recent numerical and theoretical predictions. (C) 2003 The Society of Rheology.