Development of anti-tumour necrosis factor-alpha (anti-TNF alpha) treatment offers the potential to alter radically the course of inflammatory diseases such as rheumatoid arthritis and Crohn's disease using modalities directed against a specific inflammatory mediator. Controlled randomised trials in these diseases demonstrate clinical benefit associated with significant improvement in patients with severe active joint and intestinal disease, often when conventional therapies are unsuccessful. To date, anti-TNF alpha therapy has been well tolerated and shows a favourable safety profile. This review considers the nature of this therapy and current evidence of its clinical benefit and adverse effects.