Differentiation of jaundice due to biliary tract obstruction from other types not infrequently presents a difficult problem. Existing techniques of clinical and laboratory evaluation do not always lead to correct answers, and serious errors may be made in some cases of cholestatic jaundice, viral hepatitis, and other diseases. In 1957 a new test for obstructive jaundice was described by Jirgl,1 who observed flocculation in sera of patients with obstructive jaundice while performing determination of serum mucoprotein levels. He studied this reaction in 691 sera of patients with various hepatic and nonhepatic diseases, including 46 patients with obstructive jaundice. Positive results were obtained in 95% of obstructed patients and no false positives were found among the rest. In animal experiments, sera of bile duct-ligated rats with elevated alkaline phosphatase levels gave positive reactions, while sera of normal rats were negative. A confirmatory clinical report2 appeared in 1959. Ninety sera