A novel rheometer plate was used to measure radial pressure profiles during cone-and-plate and parallel-plate shearing flows of it concentrated colloidal dispersion of poly(methyl methacryalate) spheres suspended in dioctyl phthalate. There is a long history of using suspensions of this type as a model rheological system. The measured pressure profile can be used to calculate N-1 and N-2, and also provides it check on the flow field in the rheometer. At shear rates just below onset of shear thickening, ouir measurements show that N-1 is positive as predicted by Stokesian dynamics simulations of model Brownian hard spheres, but we are unable to determine the sign of N-2. After the onset of thickening, we find that in both flow geometries the pressure increases sharply with radial position. This is in striking contrast to the pressure profiles ordinarily observed for viscoelastic liquids (with the exception of certain liquid crystal polymers), for which the pressure decreases with radial position. Under these conditions, the apparent values of N-1 and N-2, are both negative with vertical bar N-2 vertical bar > vertical bar N-1 vertical bar, as predicted by the Stokesian dynamics simulations. However, the flow in the cone-and-plate rheometer may not be viscometric after the onset of shear thickening. (c) 2006 The Society of Rheology.