OBJECTIVE Plasma of argon treatment was demonstrated to increase material surface energy leading to stronger and faster interaction with cells. The aim of the present in vitro study was to test the effect of plasma treatment on different graft materials. MATERIALS AND METHODS Synthetic hydroxyapatite (Mg-HA), biphasic calcium phosphate (BCP), cancellous and cortical xenogeneic bone matrices (CaBM, CoBM) were used representing commonly used classes of bone substitute materials. Fifty serially numbered disks with a 10mm-diameter from each graft material were randomly divided into two groups: test group (argon plasma treatment) and control group (absence of treatment). Cell morphology (using pre-osteoblastic murine cells) and protein adsorption were analyzed at all samples from both the test and control group. Differences between groups were analyzed using the Mann-Whitney test setting the level of significance at p<0.05. RESULTS Plasma treatment significantly increased the protein adsorption at all samples. Similarly, plasma treatment significantly increased cell adhesion in all groups. CONCLUSIONS Data confirmed that non-atmospheric plasma of argon treatment led to an increase of protein adsorption and cell adhesion in all groups of graft material to a similar extent. CLINICAL RELEVANCE Plasma of argon is able to improve the surface conditions of graft materials.