Thrombotic thrombocytopenic purpura (TTP) is a severe disease associated with unusually large, hemostatically hyperactive von Willebrand factor (VWF) and severe deficiency in ADAMTS-13, the protease responsible for the proteolytic degradation of VWF in plasma. ADAMTS-13 prevents inappropriate microvascular platelet aggregation by cleaving VWF between Tyr1605 and Met1606 thereby producing dimers of 176 kd and 140 kd and smaller multimers. Identification of the ADAMTS13 gene and cloning of the corresponding cDNA allowed for the application of recombinant techniques, such as genetic engineering of ADAMTS13 cDNA, cell culture expression, and in vitro activity studies to analyze the functional relationship between ADAMTS-13 and the pathophysiology of ADAMTS-13 deficiency. In vitro expression and characterization of recombinant ADAMTS-13 (rADAMTS-13) clearly established that ADAMTS-13 is deficient in congenital TTP and inhibited in acquired TTP. Recent studies have contributed greatly to our current understanding of the molecular mechanism leading to congenital and acquired TTP. Apart from being a useful tool, availability of rADAMTS-13 raised the prospect of developing a recombinant substitution therapy to improve TTP treatment and allowing present diagnostic assays to be simplified. Here we report on recent advances in cell culture expression and functional characterization of human rADAMTS-13.