A radioimmunoassay for the quantitative determination of cholic acid conjugates has been developed. Antisera were raised in rabbits injected with cholylglycine coupled by amide linkage to bovine serum albumin. The antibodies reported in this communication were not found to be mono-specific in the strictest sense. This assay is relatively simple, rapid, sensitive, reliable, and most importantly, specific for bile acids; the specificity of each antibody, however, must be thoroughly characterized at the dilution in routine use. The range of normal values for cholic acid conjugates in serum was found to be 0.1-1.6 μmol/l (mean: 0.62, ± S.D.: 0.4). © 1977.