Interleukin-6 (IL-6) is a member of the family of cytokines collectively termed "the interleukin-6 type cytokines." Among its many functions, IL-6 plays an active role in immunology, bone metabolism, reproduction, arthritis, neoplasia, and aging. IL-6 expression is regulated by a variety of factors, including steroidal hormones, at both the transcriptional and post-transcriptional levels. IL-6 achieves its effects through the ligand-specific IL-6 receptor (IL-6R). Unlike most other cytokine receptors, the IL-6R is active in both membrane bound and soluble forms. Defining mechanisms to control IL-6 or IL-6R expression may prove useful for therapy of the many clinical disorders in IL-6 plays a role.