A method and a cooling system for cooling blades of at least one blade row in a rotary flow machine includes an axial flow channel which is radially limited on the inside by a rotor unit and at the outside by at least one stationary component, the blades are arranged at the rotary unit and provide a shrouded blade tip facing radially to said stationary component. Pressurized cooling air is fed through from radially outside towards the tip of each of said blades in the at least one blade row, and the pressurized cooling air enters the blades through at least one opening at the shrouded blades' tip.