We compared a radioimmunoassay and an enzymatic method to measure plasma bile acid concentrations of chickens and 5 psittacine genera. The 2 assays compared well with r² values ranging from 0.77 to 0.92. The radioimmunoassay was linear to 50 μmol/L, and the enzymatic method, to 200 μmol/L. When measured by the enzymatic method, bile acid concentrations were decreased in the presence of hemolysis and falsely increased in the presence of lipemia and high concentrations of lactate dehydrogenase. Results for both assays showed only small changes when samples were stored at −20°C and −70°C; however, storage at 4°C resulted in decreases in bile acid concentrations that were greater than 50% after 4 days. An advantage of the enzymatic method is that it can be performed more quickly than the radioimmunoassay and without the special procedures and guidelines applying to use of radioisotopes. However, the radioimmunoassay requires lower sample volumes (50 μl of plasma) than the enzymatic method (up to 400 μl unless the assay has been specifically adapted) and is not affected by hemolysis, lipemia, or elevated LDH concentrations. Others have found both assays to have adequate precision and accuracy. Therefore, the advantages and disadvantages of each should be weighed when selecting assay method. Clinicians should use assay-specific reference ranges as well as the same laboratory for paired determinations from the same patient.