Various extracts of the vinelike plant Tripterygium wilfordii Hook f have been widely used in China to treat patients with a number of autoimmune diseases. Although most of the clinical experience has derived from uncontrolled trials, one placebo-controlled double-blind trial has clearly demonstrated efficacy in rheumatoid arthritis. Studies in laboratory animals have indicated that extracts of Tripterygium wilfordii Hook f suppress both immune and inflammatory responses and also effectively treat a number of models of autoimmune disease. More detailed in vitro analysis has indicated that components of Tripterygium wilfordii Hook f suppress immune responses by inhibiting transcription of cytokine genes, including interleukin-2 and gamma interferon. The current status of knowledge of the potential clinical benefit of this herbal remedy and possible mechanisms accounting for its utility are considered in this review.