AbstractThis study describes the collagen‐I coating of titanium and steel implants via cold low‐pressure gas plasma treatment. To analyze the coatings in terms of biocompatibility osteoblast‐like osteosarcoma cells and human leukocytes were cultivated on the metal surfaces. Two different implant materials were assessed (Ti6Al4V, X2CrNiMo18) and four different surface properties were evaluated: (a) plasma pretreated and collagen‐I coated implant materials; (b) collagen‐I dip‐coated without plasma pretreatment; (c) plasma treated but not collagen‐I coated; (d) standard implant materials served as control. The different coating characteristics were analyzed by scanning electron microscopy (SEM). For adhesion and viability tests calcein‐AM staining of the cells and Alamar blue assays were performed. The quantitative analysis was conducted by computer assisted microfluorophotography and spectrometer measurements. SEM analysis revealed that stable collagen‐I coatings could not be achieved on the dip‐coated steel and titanium alloys. Only due to pretreatment with low‐pressure gas plasma a robust deposition of collagen I on the surface could be achieved. The cell viability and cell attachment rate on the plasma pretreated, collagen coated surfaces was significantly (p < 0.017) increased compared to the non coated surfaces. Gas plasma treatment is a feasible method for the deposition of proteins on metal implant materials resulting in an improved biocompatibility in vitro. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010