A　weight　function　method　for　the　determination　of　the　critical　plane　is　here　proposed　for　the　case　of　specimens　under　combined　bending　and　torsion　in　the　high　cycle　fatigue　regime.　The　critical　plane　is　assumed　to　be　coincident　with　the　mean　maximum　absolute　shear　stress　plane,　which　is　calculated　by　averaging　the　instantaneous　angle　between　the　specimen　axis　and　the　normal　to　the　maximum　absolute　shear　stress　plane.　Two　kinds　of　weight　functions　are　proposed　to　determine　such　a　plane.　The　proposed　method　to　determine　the　critical　plane　is　verified　by　employing　fatigue　data　available　in　the　literature　in　terms　of　experimental　fracture　planes,　and　the　multiaxial　fatigue　life　is　also　predicted　by　a　reformulation　of　the　criterion　proposed　by　Carpinteri　et　al.　to　verify　the　determined　critical　plane.　The　results　show　that　the　proposed　method　can　be　applied　to　determine　the　critical　plane　under　both　constant　and　variable　amplitude　loading.　(C)　2016　Elsevier　Ltd.　All　rights　reserved.