Ten episodes of severe pyogenic infection occurring in nine patients with rheumatoid arthritis are reported. There was a wide range of presenting features including pyoarthrosis in 7 episodes. Three cases presented with meningitis, bacterial endocarditis and probable multiple abscesses respectively. Infection was caused by Staphylococcus aureus in 7 episodes and by Staphylococcus epidermidis, Streptococcus pneumoniae and beta-haemolytic Streptococcus in each of one episode. Three infective episodes were fatal. Pyogenic, especially staphylococcal, infection should be considered in patients with rheumatoid arthritis with unexplained illness with or without sudden deterioration in joint symptoms. It is important to recognize and treat infection rapidly.