Radial flow between parallel surfaces produces a spatially dependent wall shear stress that permits investigation of cell adhesion for a range of shear simultaneously. The maximum for this range is limited by accurate prediction of fluid mechanics at small radial positions. Numerical and analytical models for predicting fluid mechanics demonstrate that corner and inertial effects at small radial positions are not only significant but differ with the direction of flow (i.e., converging us. diverging). For diverging flow fr om an axially oriented inlet, the recirculation zone downstream of the corner disturbs streamlines at small radial positions. With converging pow this recirculation zone is confined to the axially oriented outlet. Also, inertia contributes positively for converging pow, enhancing the magnitude of shear stress, but negatively for diverging flow. Experiments with cells support the validity of this analysis : the strength of cell adhesion does not vary with direction or magnitude of flow.