Cytokines play an important role in defining the fate of cells, such as proliferation, differentiation or death. Distinct responses of target cells to cytokines are determined by specific signal transduction events. The group of interleukin-6-type cytokines comprises also: interleukin-11 (IL-11), oncostatinM (OSM), leukemia inhibitory factor (LIF), ciliary neurotrophic factor (CNTF) and cardiotrophin-I (CT-I). IL-6-type cytokines use pl30 as a common b chain of their multimeric receptor complexes. Binding of the ligands leads to the activation of Jak tyrosine kinases, which in tum phosphorylate intracellular part of the receptor and initiate various signal transduction events mediated by STAT factors, SHP-2 phosphatase or Src-family kinases. The signalization by Jak/STAT pathway is negatively regulated by dephosphorylation or synthesis of the specific inhibitors like PIAS or SOCS/SSI/JAB. The outcome ofthe signal transduction seems to be an effect of the interplay among the contradictory signaling pathways simultanously activated via cytokine receptor.