Iridium oxide is an attractive material for the development of novel multi electrode array (MEA) systems that provide electrodes for stimulation as well as recording single neurons. In this study the biocompatibility of pure iridium and different iridium oxides that differ characteristically in their surface roughness was investigated using two different biological test systems, insect and vertebrate neurons. Iridium oxide surfaces were coated with Concanavalin A and poly-(D)-lysine. In detailed investigations (R(a) value determination, contact angle measurement, marker enzyme assay) the surface characteristics of non-modified and coated iridium oxide films were analysed, demonstrating that the materials can be successfully coated. Furthermore, we show that locust neurons grow well on all substrates tested, while chicken neurons need coated surfaces for proper adhesion. Increasing the roughness of iridium oxide films, which in principle could improve cell adhesion, did not improve the neurocompatibility. These results show that in future applications iridium oxide films can be used with surface morphologies previously shown to be optimal for stimulation purposes (cauliflower-like surface structure).