The inability to successfully position angioplasty catheters and the occurrence of complications during angioplasty procedures can, in part, be related to the shear forces generated during catheter introduction. Shear forces are the axial contact forces that the catheter system exerts on the inner arterial surfaces during advancement. The shear forces exerted by three different catheter designs (coaxial dilator, coaxial balloon, and linear extrusion) were measured in normal and atherosclerotic arteries; in modeled stenoses of variable severity, length, and compliance; and in modeled vessel angulations. The results with modeled vessels show that the linear extrusion catheter reduces the level of shear forces, particularly in narrow, long, noncompliant stenoses and in tortuous vessels. The stenotic artery results also show that the linear extrusion catheter minimizes these forces in tight lesions. The relative differences in forces are explained by the mechanism of action for each catheter. The reported occurrences of technical difficulties, complications, and long-term patency rates are then interpreted on the basis of the relative differences in measured shear forces. The results of this study combined with preliminary clinical data indicate that linear extrusion should facilitate placement and reduce associated complications.