The aetiology of systemic, autoimmune, chronic inflammatory diseases — such as rheumatoid arthritis — is not known, and their pathogenesis is complex and multifactorial. However, progress in the characterization of intercellular mediators — proteins that are now known as cytokines — has led to the realization that one cytokine, tumour-necrosis factor (TNF; previously known as TNF-α), has an important role in the pathogenesis of rheumatoid arthritis. This discovery heralded a new era of targeted and highly effective therapeutics for rheumatoid arthritis and, subsequently, other chronic inflammatory diseases.