Platelet adhesion in the annular perfusion system developed by Baumgartner was studied under pulsatile, oscillatory, or steady flow conditions. To investigate in what way pulsatile flow affects platelet adhesion, we developed a flow system that produces a sinusoidal laminar flow superimposed on a constant component in the annular perfusion chamber. Frequencies and amplitudes of this sinusoidal flow were in the physiological range. Pulse frequencies varied between 30 and 120 beats/minute, and different amplitudes of the wall shear rate in the range 75 to 1000 s-1 were studied. Shear rates resulting from the constant flow component were between 500 s-1 and 1800 s-1. Under these conditions, no significant differences in platelet adhesion were observed between steady flow and pulsatile flow. In the case of an oscillatory flow (absence of constant component), a clear dependence of platelet adhesion on the amplitude of the pulse was seen. These data indicate that platelet adhesion in larger blood vessels, such as the aorta and larger arteries where backflow is limited, is not essentially influenced by the pulsatility in these vessels.