Titanium with its natural oxide is known to be generally good biocompatible; and therefore, the suitability of some Ti-based coatings as coating for blood-contacting implants is analyzed. Layers of pure Ti, Ti oxynitrides (TiN1-xOx with x = 0.25, 0.50, and 0.75), and Ti oxides were deposited on oxidized Si from a plasma produced by cathodic arc evaporation under addition of N-2 and/or O-2 to the ambient near the substrate. The oxynitrides are crystalline with the fcc structure of TiN up to x = 0.25. For x = 0.5, a two-phase system of fcc TiN and fcc TiO has been found. In dependence on the deposition parameters, amorphous and crystalline layers (anatase + brookite or rutile) of TiO2 have been obtained. The rutile layers were doped by implantation of P. The amorphous TiO2 layers were implanted with Cr. To study the correlation between structure of the coating and blood compatibility, the clotting time of blood plasma as well as the adhesion and activation of blood platelets on the surface was investigated. TiN and oxynitrides showed the longest clotting time compared to rutile. Minimum platelet adhesion has been observed for pure TiO2. Contrasting tendencies in the dependence of clotting time and platelet adhesion on the microstructure have been stated. However, for P+-doped rutile, both enhanced clotting time and improved platelet adhesion were observed. Platelet adherence and activation always showed similar trends. (C) 2004 Elsevier B.V. All rights reserved.