A HIGH-PURITY SOLUBLE THROMBOMODULIN WHICH IS PRODUCED BY A TRANSFORMANT, SAID TRANSFORMANT HAVING BEEN OBTAINED BY TRANSFECTING A HOST CELL WITH DNA COMPRISING A BASE SEQUENCE ENCODING SOLUBLE THROMBOMODULIN, AND CONTAINS LESS THAN 10 NG OF HOST CELL-DERIVED PROTEINS PER 10,000 U OF THE SOLUBLE THROMBOMODULIN.