In the early 1930s Jorpes began work on the isolation and structure of heparin. In 1936 he successfully purified heparin and subsequently demonstrated that it was localized in the mast cells of tissues. In the same year Jorpes and the surgeon Clarence Crafoord used heparin to prevent postoperative thrombosis. Jorpes provided further confirmation of the effectiveness of heparin in the treatment of thrombosis in the second edition of this work published in 1946.