Polymer materials for the veneers o f fixed prostheses commonly require retention elements on metal framework, because there is no chemical adhesion. The use o f retention elements, however, is related to certain problems and the lack o f chemical bond allows the creation o f marginal gaps at the resin - metal interface, due to the different thermal expansion coefficients of the two materials. The development o f the chemical resin - to metal bonding could resolve this problem and also reduce the need for mechanical retention on metal frameworks. The aim o f this study was to evaluate the bond strength o f two current systems after wet storage and intesive thermocycling program. Two resin to metal bonding systems were tested: Silicoater MD - Dentacolor and rtglass - Kevloc. Three dental alloys were used: Wiron 99 (Ni - Cr, Bego Co.), Wirolloy (Ni - Cr, Bego Co.) and Wirobond C (Co - Cr, Bego Co.). The bond strengths between resin and metal were determined by the use of the four - point flexure test (4 FPBT). Before this, all the samples were subjected to a thermocycling program that included 1500 thermal cycles between 5°C - 55°C. This study indicated that the Silicoater MD - Dentacolor system can provide stable bonding o f resin to metal substructures. On the other hand, the Artglass - Kevloc system demostrated bond failures after thermocycling and indicated unstable bonding or weak bond strengths. For this system, additional in vitro research is required to investigate the mechanism o f bond weakening after thermocycling.