Starting from the first steam injection cycles (GE-STIG; Cheng), the technique of increasing gas turbine performances by injecting water/steam somewhere before the combustion chamber, has shown very interesting results for power and efficiency increase and for NO, emissions. Very interesting performances are achieved by evaporative cycles, such as the HAT (Humid Air Turbine), which is capable of achieving 50% conversion efficiency with lower investment costs compared to combined cycles. Other advantages of the steam injected cycle include the power modulation that is possible by varying the injected steam flow rate, keeping the maximum temperature constant. In particular, for the HAT cycle, it is possible to choose different temperature, pressure and compositions for the blade cooling fluid, depending on the bleed point. In this paper, a second law analysis of the HAT cycle and its components, has been performed. In particular, the exergetic analysis of blade cooling has been carefully analysed.