The effect of shear stress on the ability of tissue factor-factor VIIa complex to activate factor X in a continuous flow reactor was studied. Tissue factor immobilized in a phospholipid bilayer on the inner surface of a capillary tube was exposed to a perfusate containing factors VIIa and X flowing at flow rates of 12.7, and 204 mu l/min, corresponding to wall shear rates of 100, and 1760 sec(-1). The maximum flux (moles formed per unit surface area per unit time) of factor Xa (activated form of factor X) produced at the wall decreased as the shear stress at the wall was increased from 1 to 3 dynes/cm(2) (3-fold) at a constant shear rate of 100 sec(-1). In contrast, at higher shear rate (1760 sec), increasing shear stress from 16 to 48 dynes/cm(2) had no significant influence on factor Xa production. The decreased production of factor Xa at higher shear stress (low shear rate 100 sec(-1)) probably reflects the transport limitation of factor X to the wall. Apparently shear stress can directly influence the activation of factor X at low shear rates.