Abstract: Disclosed are fluorogenic substrates for measuring ADAMTS13 activity or ADAMTS13 inhibitor activity. Substrates can comprise an oligopeptide which can consist of up to 80 amino acids of sequence of von Willebrand Factor (VWF). The oligopeptide can include modifications of sequence of VWF, including an amino-terminal glycine, a scissile Y-M peptide, and a cysteine substitution located from 1 to 12 amino acids from the scissile Y-M in the carboxy terminal direction. A substrate can further comprise a fluorophore and a fluorescence quencher bound to the oligopeptide on opposite sides of the scissile Y-M peptide, wherein the fluorescence quencher is not identical to the fluorophore. An oligopeptide can be encoded by a nucleic acid sequence which can also encode a His tag. An oligopeptide can be expressed in a cell or microorganism. Also disclosed are methods of using a fluorogenic substrate to measure ADAMTS13 activity or ADAMTS13 inhibitor activity.