The potentiometric and impedance characteristics of various selective Ca2+polymeric membranes are described and interpreted by theory and experiments for Ca2+microfabricated sensor arrays. These are designed for further biomedical applications with an emphasis on potentialin situapplications. The polymeric materials used in the present studies consist of either carboxylated PVC or aliphatic polyurethane. Both materials showed good adherence properties to the polyimide-coated Kapton substrate used in planar sensor fabrication. The impedance analysis, performed in the frequency range from 65,000 Hz to 0.1 Hz, revealed the bulk geometrical response at high frequencies. Measured Rbulkcorresponds to the unperturbed bulk resistance. That, in turn, depends on mobilities and concentrations of Ca2+complex and mobile sites. Decreases in Rbulkcorrelated well with sensor behavior during the preconditioning (hydration) period. Studies of blood interactions with these sensors proved that the main sensor characteristics (E0, slope of the calibration curve, and reproducibility of response) are not significantly affected after 14 days of whole blood contact.