Shear stress induces not only platelet aggregation but also platelet-tumor cell interaction.
 To investigate the interaction between platelets and tumor cells under well-defined flow conditions, the effect of tumor cells on platelet aggregation induced by shear stress was studied using a cone and plate viscometer adapted for measuring transmitted light intensity.
 Aggregation was markedly enhanced by HMV-1 cells in a cell number-dependent fashion under shear stress of 12 dyne/cm2.
 Enhancement was not observed at a high shear stress of 108 dyne/cm2.
 A monoclonal antibody against GPIIb/IIIa, 7E3 completely abolished enhancement of aggregation by HMV-1.
 Apyrase had similar inhibitory effects.
 Scanning electronmicroscopy showed that direct contacts of platelets with HMV-1 cells could be demonstrated when platelet-platelet interaction was inhibited by 7E3 or apyrase.
 These results may indicate that, at a shear stress of 12 dyne/cm2, direct contacts of platelets and HMV-1 cells may trigger enhancement of platelet aggregation.
