The present invention relates to a disintegrin and metalloproteinase containing thrombospondin 1-like domains (ADAMTS) and in particular to a novel ADAMTS13 protease and to nucleic acids encoding ADAMTS13 proteases. The present invention encompasses both native and recombinant wild-type forms of ADAMTS13, as well as mutant and variant forms including fragments, some of which posses altered characteristics relative to the wild-type ADAMTS13. The present invention also relates to methods of using ADAMTS13, including for treatment of TTP. The present invention also relates to methods for screening for the presence of TTP. The present invention further relates to methods for developing anticoagulant drugs based upon ADAMTS13.