Accumulating evidence has demonstrated that cytokine receptor signaling is negatively regulated by a family of Src homology 2 domain-containing adaptor molecules termed SOCS (Suppressor of Cytokine Signaling) (1-3). Currently, there are eight members of the SOCS family that have been recognized, SOCS-1, -2, -3, -4, - 5, -6, -7 and CIS. Structurally, the SOCS proteins are composed of an N-terminus region of variable length and amino acid composition, a central SH2 domain, and a previously unrecognized C-terminus motif that has been called the SOCS box (4). The SOCS proteins appear to form part of a classical negative feed back loop that regulates cytokine signal transduction via a STATinduced transcriptional mechanism (5). Transcription of each of the SOCS genes occurs rapidly in vitro and in vivo in response to cytokines, and once produced, the various members of the SOCS family appear to inhibit signaling in different ways. Within the SOCS subfamily, SOCS-4, SOCS-5, SOCS-6, SOCS-7 remain poorly understood (6). On the basis of structural considerations, it would be expected that SOCS-4, -5, -6, and -7, like SOCS-1, SOCS-2, SOCS-3 and CIS, act to negatively regulate signal transduction (4), but it is uncertain which specific cytokine is involved (7-9).Synonyms: SOCS-4, SOCS-7, SOCS7, Suppressor of cytokine signaling 4, Suppressor of cytokine signaling 7