PURPOSE: A product obtained by the combination of a novel urea compound with a high-molecular-weight protein is used as an antigen to prepare said antiserum for the radioimmunoassay for Glibenclamide, an oral hypoglycemic.

CONSTITUTION: A product obtained by the combination of p-aminobenzamide- ethyl-benzenesulfonyl-N-cyclohexylurea of the formula with a high-moleuclar-weight protein such as cow serum albumin is used as an antigen to prepare said antiserum for Glibenclamide radioimmunoassay. It is very difficult to measure the concentration of Glibenclamide, an oral hypoglycemic of sulfonylurea, in blood because the appropriate dosage is only 2.5mg every once. The antiserum that is prepared by using Glibenclamide as an antigen is extremely specific to Glibenclamide to enable the Glibenclamide radioimmunoassay with sensitivity as high as 50pg.