In current microprocessors and systems, an increasingly high silicon portion is derived through automatic synthesis, with designers working exclusively at the RT-level, and design productivity is greatly enhanced. However, in the new design flow, validation still remains a challenge: while new technologies based on formal verification are only marginally accepted, standard techniques based on simulation are beginning to fall behind the increased circuit complexity. This paper proposes a new approach to simulation-based validation, in which a Genetic Algorithm helps the designer in generating useful input sequences to be included in the test bench. The technique has been applied to an industrial circuit, showing that the quality of the validation process is increased.