The human IL-1 receptor antagonist (IL-1ra) was produced in a high yield E. coli expression system, and was purified in a rapid two-step purification, This recombinant IL-1ra molecule possessed full binding activity to the IL-1 receptor (type I) and totally inhibited IL-1-induced PGE 2 production by human dermal fibroblasts. Radioalkylation and analysis of V8-derived IL-1ra peptides indicate that the four cysteines present in the IL-1ra are not disulphide-linked.