Interleukin-6 (IL-6) is a multifunctional cytokine that plays roles in regulating immune responses, acute phase reactions and hematopoiesis. IL-6 signaling is regulated by two receptors, a specific alpha chain (IL-6Ralpha) and a signal transducer, gp130. In this study, cDNA encoding the 445 amino acid propeptide of chicken IL-6Ralpha (chIL-6Ralpha) was identified. The predicted 445 amino acids showed approximately 40% sequence identity with mammalian homologues. In a domain search, chIL-6Ralpha had a signal peptide of 20 residues, an immunoglobulin-like (IG) domain of 71 residues and a fibronectin-type III (FN III) domain of 85 residues. On comparison with mammalian homologues, four conserved cysteine residues and the WSXWS motif were observed in the N- and C-terminal regions of the FN III domain, respectively. Expression analysis revealed that chIL-6Ralpha is strongly expressed in liver and the chicken hepatoma cell line LMH. These findings indicate that the identified chicken cDNA sequence encodes a chIL-6Ralpha homologue.