A monoclonal antibody (Mab) developed against a partially purified bursal protein extract was found to bind specifically to a single cell type in the cortico-medullary border region of the chicken bursa of Fabricius. These cells were microscopically similar to the bursal secretory dendritic-like cells. A product with an apparent molecular weight of approximately 56 kDa on SDS-polyacrylamide gel electrophoresis was immunopurified from bursal extracts by utilizing this Mab. This product was subjected to peptide digestion and protein sequencing. The two resulting sequences perfectly matched the known sequence of chicken ovoinhibitor. Gene-specific polymerase chain reaction (PCR) primers were designed for the ovoinhibitor, RNA was purified from chicken bursae, and reverse transcription/PCR was performed. Two amplicons with the expected size for ovoinhibitor mRNA were obtained. These data suggest that the gene for ovoinhibitor is expressed in the bursa of Fabricius, and that the bursal secretory dendritic-like cells may be a previously unreported source of ovoinhibitor.