Eight cases of septic arthritis occurring in patients with rheumatoid arthritis are reviewed. The difficulty in diagnosis of this condition is due in part to a failure of these patients to respond normally to infection. Consequently patients often present late in the course of their septic episode and treatment is often delayed. The importance of early diagnosis and treatment of the infection is stressed by the high mortality rate in this group of patients. Many factors operate to encourage infection in rheumatoid arthritis and the current concepts of the problem are reviewed.