Tests for total bilirubin on 10 icteric sera by 5 diazo procedures and a spectrophotometric method showed fair agreement with most samples but an occasional grossly discrepant result. Results for free and conjugated bilirubin by diazo methods, acetone precipitation, and extraction of serum with ethyl acetate and chloroform were widely discrepant. Problems in documentation of accuracy of such procedures are discussed. It is concluded that unavailability of reference standards of bilirubin conjugates poses a serious obstacle to solution of the analytical problems.