Designers of safety-critical VLSI systems are asking for effective tools for evaluating and validating their designs. Fault Injection is commonly adopted for this task, and its effectiveness is therefore a key factor. In this paper we propose to exploit FPGAs to speed-up Fault Injection for fault tolerance evaluation of VLSI circuits. A complete Fault Injection environment is described, relying on FPGA-based emulation of the circuit for fault effect analysis. The proposed approach allows combining the efficiency of hardwarebased techniques, and the flexibility of simulation-based techniques. Experimental results are provided to support the feasibility and effectiveness of the approach.