The development of planar electrochemical multi-sensors for simultaneous determination of dissolved ions such as chloride, dissolved oxygen and electrical conductivity for the application, e.g. in biological liquids is reported. In this context, new and improved functional materials have been developed and technologies have been optimized in order to prepare micro sensor structures. Thick film and dispenser techniques were applied to print sensor structures and immobilized ionophores as well as reference systems. Sensor tests showed that the results are comparable to those of conventional sensors. With respect to a user-friendly calibration of different types of sensors, multi-buffer solutions have been developed for various sensor combinations. (C) 2004 Elsevier Ltd. All rights reserved.