PURPOSE: To accurately determine free urokinase blocking factors by combining carrier agglutination blocking reaction using an urokinase sensitizing carrier and an antiurokinase antibody, and a carrier agglutination reaction method using an antiurokinase antibody sensitizing carrier.

CONSTITUTION: Urokinase and urokinase blocking factors exist in urine, blood, etc., in the state that they are bound to each other or the excess portion of either of these is free. An urokinase sensitizing carrier (the carrier is a red blood cell or the like) has the minimum agglutination blocking concn. of respective corpus libera of urokinase or urokinase blocking factors in the presence of an antiurokinase antibody. Hence, the minimum agglutination blocking concn. of urokinase and its blocking factors is known beforehand with a sample of a known concn., thence the agglutination reaction of the specimen liquid and an urokinase sensitizing body is attempted, whereby a minimum agglutination blocking concn. is determined. Next, the specimen liquid and the antiurokinase antibody sensitizing carrier are caused to react, and if agglutination occurs, it indicates that the above-described blocking factors exist. The concn. of the blocking factors is calculated from the dilution of the specimen liquid and the minimum agglutination blocking concn. having determined beforehand.