Liquid failure has been observed in low Reynolds number (Stokes) shear flows where reduction of the hydrodynamic pressure should not occur. Cavitation in Stokes flows has implications in lubrication, polymer processing, and rheological measurements. Such cavitation can be predicted by a principal normal stress cavitation criterion (PNSCC). We present results of a direct experimental test of the PNSCC. Imaging of the cavitation events suggests that the cavitation is gaseous and originates from preexisting nuclei. Crevice-stabilized gas nuclei are assumed, and numerical simulations are used to investigate the cavitation event for a Newtonian liquid. The inception of cavitation from a preexisting nucleus, the persistence of suitable nuclei, and the growth and deformation of shed bubbles are considered. (c) 2005 American Institute of Chemical Engineers