AbstractThe exposure of a biomaterial to blood gives rise to complex reactions playing an important role in many biological phenomena, such as the problem of biocompatibility and the mechanism of cardiovascular and thromboembolic diseases. In the present work, we use a frequency‐domain dielectric spectroscopy approach to evaluate possible changes in the passive electrical parameters of the erythrocyte membrane, i.e., the membrane conductivity σ_s and the membrane permittivity ϵ_s, after the insertion of a prosthesis (mean implantation time 8 days) in the circulatory system of patients treated for aortic aneurysm and the consequent interactions of erythrocyte cells with the biomaterial surface. We observe an increase of both the membrane conductivity and membrane permittivity, indicating changes at molecular level in the structural organization of the membrane. These membrane alterations can be viewed as precursory events for the initiation of the complex sequence of enzymatic reactions that take place on the material surface. Our results, although preliminary imply that a direct interaction between erythrocyte cell membrane and vascular prostheses may occur, causing a marked alteration in the electrical properties of the cell membrane. These findings might have relevant clinical implications and might offer possibilities to predict biocompatibility of biomaterials and give some further suggestions to resolve the problem of biomaterial‐associated thrombogenicity. © 2001 Wiley Periodicals, Inc. J Biomed Mater Res 59: 100–109, 2002