For large off-shore wind turbines, blades with relative low blade mass are becoming more important. The economic use of large-tow carbon fibers can help achieve lower blade masses. Basic material design data have been established for two promising material combinations, including the fatigue properties for Panex33/epoxy. Blade root joints have been developed in a carbon/glass combination, resulting in a better price performance ratio. The initial cost assessment on a blade dominated by severe fatigue loads shows that application of carbon fibers in the spar leads to cost reductions.