Etanercept (Amgen Inc, Thousand Oaks, CA) is a human soluble p75 tumor necrosis factor (TNF) receptor-human-IgG1 (hup75 TNFR-huIgG1) fusion protein used in the treatment of chronic inflammatory diseases in humans, including rheumatoid arthritis, juvenile rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis, and psoriasis. To be able to study the effects of the soluble receptor fusion protein in mouse models, including those that mimic human granulomatous infections, a murine soluble p75-TNF receptor-murine IgG1 (murine p75-murine IgG1) fusion protein had to be constructed. This article discusses the generation, large-scale production, and purification of this molecule.