We are using optimized variations of a force-free single-molecule technique, known as Tethered Particle Motion (TPM) to study protein folding/refolding in their natural form. This method enables us to track the folding and unfolding of single polypeptide chains composed of I27 tandem repeats using either chemical denaturation (force-free) or force unfolding using flow or AFM. We can quantitatively characterize the end-to-end distance of the single polypeptide chain as it unfolds and refolds.