Interleukin-1 (IL-1) is a pro-inflammatory cytokine that exerts a wide range of biological effects. The recently identified IL-1 receptor antagonist (IL-1ra) has provided a tool for blocking IL-1 activity in vivo, leading to a detailed understanding of the role of this cytokine in the inflammatory response. The importance of IL-1 production in glomerulonephritis has been shown by the ability of IL-1ra treatment to suppress the induction and progression of experimental crescentic glomerulonephritis. Although further studies are required, IL-1ra treatment is an attractive adjunct therapy for patients with progressive glomerulonephritis.