With the discovery that the cat is susceptible to infection by a lentivirus quite similar to the virus that causes the human acquired immune deficiency syndrome, the cat has become an important animal model with which the interactions between host and immunodeficiency virus can be studied. To facilitate investigation of the feline immune response and the response of cytokine expression to infection by feline immunodeficiency virus, our laboratory has focused on the isolation and molecular cloning of cDNA representative of feline lymphokines, cytokines, and monokines. Herein, we describe the molecular cloning and characterization of a cDNA encoding feline interleukin (IL)-6. The nucleotide sequence of feline IL-6 was found to exhibit 81%, 76%, 63%, and 61% homology with pig, human, rat, and mouse IL-6, respectively, while the predicted amino acid sequence exhibits 66%, 53%, 37%, and 30% homology with pig, human, rat, and mouse IL-6, respectively.