Reseeding is used to improve fault coverage in BIST pseudo-random testing. Most of the work done on reseeding is based on storing the seeds in an external tester. Besides its high cost, testing using automatic test equipment (ATE) makes it hard to test the circuit while in the system. In this paper, we present a technique for built-in reseeding. Our technique requires no storage for the seeds. The seeds are encoded in hardware. The seeds we use are deterministic so 100% fault coverage can be achieved. Our technique causes no performance overhead and does not change the original circuit under test. Also, the technique we present is applicable for transition faults as well as single-stuck-at faults. Built-in reseeding is based on expanding every seed to as many ATPG patterns as possible. This is different from many existing reseeding techniques that expand every seed into a single ATPG pattern. This paper presents the built-in reseeding algorithm together with a hardware synthesis algorithm and implementation.