A 39-year-old woman with long-standing seropositive rheumatoid arthritis who had a total replacement of her left knee with a modular prosthesis in 1994 presented with fever, pruritic rash, and acute synovitis of that joint following local trauma. Synovial fluid showed a charcoal-like color, and contained abundant phagocytes laden with metal particles. In patients with rheumatoid arthritis who have undergone total joint replacement, metal particle reactions and possible hyper-sensitivity should be added to the list of potential causes of superimposed acute synovitis and systemic manifestations.