Interleukin (IL)-1beta-encoding regions of chicken, duck, goose, turkey and pigeon were cloned and sequenced. Each IL-1beta-encoding region of chicken, duck, goose and turkey is 804 nucleotides long and encodes IL-1beta protein that is 268 amino acids. Pigeon IL-1beta-encoding region is 810 nucleotides long and encodes IL-1beta protein that is 270 amino acids. Two one-nucleotide and one four-nucleotide insertions of pigeon IL-1beta-encoding region sequence were found, resulting in two amino acid insertions in pigeon IL-1beta. Pairwise sequence analysis showed that the sequence identities of IL-1beta-encoding genes ranged from 77% to 99%, which were also found for IL-1beta protein sequence identities, with an average level of both sequence identities of 89%. Phylogenetic analysis indicated that IL-1beta-encoding regions and the encoded proteins of chicken, duck, goose and turkey clustered together and evolved into a distinct phylogenetic lineage from that of pigeon which evolved into a second lineage. The results from the binding reaction of antiserum against each recombinant IL-1beta (r IL-1beta) protein to homologous or heterologous rIL-1beta, the enhancement levels of K60 mRNA expression in rIL-1beta-treated DF-1 cells or the reduction levels of K60 mRNA expression in DF-1 cells treated with rIL-1beta that was preincubated with homologous or heterologous antiserum showed that all five rIL-1beta were functional active and shared significantly structural and functional homology.