there is a wealthy literature on bonding strength of composites to dentine. one of the reasons for the large number of studies is the continuous introduction of new bonding agents in combination with accumulated knowledge about the dentine substrate conditions. the aim of the present study was to compare the "in vitro" tensile bond strengths of two dentine bonding systems (3m and kerr) applied to different dentine roughness (220 and 600 grit)and two sizes of bonding areas (3,14 mm2 and 12,56 mm2). different storage conditions (initial and final) were also considered. one hundred and sixty human teeth were randomly allocated in 4 groups. the kerr system groups and the smallest bonding area groups showed the highest tensile strengths. the storage condition and the substrate roughness did not display a significant influence on bond strengths.