In this paper we experimentally investigate the efficiency of concurrent checking for the AES encryption algorithm (Rijndael) by parity modification according to . Also we propose a simple new BIST method. For BIST the implementation of the AES algorithm itself is used as well as a pseudo-random test input generator and a compactor of the test results. Thereby we utilized the property of the AES algorithm that arbitrarily given plain texts are encrypted by the successive rounds into "pseudo-random" cipher texts which are the (test) inputs for the next round. The complete data path of the AES algorithm is simulated as a netlist of AND-, NAND-, OR-, NOR- and XOR-gates. All possible single stuck-at faults are injected and simulated. For a special implementation of the S-boxes all errors within the datapath of the AES algorithm due to single stuck-at faults are immediately detected.