1. Chicken IgA purified from biliary fluids was chemically and immunologically characterized. 2. Chicken IgA was determined to be the only immunoglobulin class present in bile. Gel filtration studies reveal polymeric IgA e.g. 17-19S. 3. Antigenically, chicken IgA is distinct from chicken IgG, and IgM. 4. Chicken IgA does not show antigenic homology to human IgA. 5. SDS poly-acrylamide gel electrophoresis revealed IgA to possess heavy chains of 60,000 and light chains of 24,000 mol. wt, respectively. 6. Peptide mapping of tryptic digests of chicken alpha chains reveals approximately 35 peptides. The peptide map pattern is distinct from chicken gamma chains.