This study aims to determine the influence of shear stress on cell cultures under carefully controlled conditions. Human embryonic kidney cells grow^as an attached, confluent monolayer on a flat substrate were subjected to steady, uniform laminar flow in a specially designed flow chamber, in which shear stress was precisely defined and controlled. Experiments performed for shear stresses ranging from .2 to 6. N/m, with a varied shear stress exposure time from 2 to 24 hours. The influence of the shear field was slight at low shear stress (.26 N/m) but it had a dramatic effect on cell morphology at higher shear stresses (above 2.6 N/m ) and long exposure times (24 hours). It was also found that shear stress and time stimulated the release of urokinase enzyme. The significance of such flow studies is presented in relation to their possible use for biosynthesis of urokinase enzyme by kidney epithelial cells/