Tumor necrosis factor alpha (TNF-alpha) is a pleiotropic cytokine with strong proinflammatory and immunomodulatory properties. TNF-alpha plays a critical role in many acute or chronic inflammatory diseases and anti-TNF strategies have proven to be clinically effective. Two TNF-specific cell surface receptors, TNF-R1 (p60) and TNF-R2 (p80), have been identified and the function of these receptors and the downstream intracellular signal-transduction pathways have been extensively studied in vitro. For a long time p60 was considered to be the predominant mediator of TNF signaling, whereas p80 was ascribed only an auxilliary function. However, there is increasing clinical and experimental evidence for an important independent role of p80 signaling in chronic inflammatory conditions. To date, most data exist for Crohn's disease. Upregulation of p80 and increased p80 signaling aggravates experimental colitis and is likely to contribute to the chronicity of inflammation in vivo. Further studies are required to elucidate critically important steps in TNF signaling that might be dysregulated. This will lead to a better understanding of the pathogenesis of these diseases and potentially reveal new, more specific therapeutic targets.