Infections are common in patients with rheumatic disorders. Reasons for such vulnerability include alterations of immunoregulation, disease severity, debility, co-morbid illnesses and the use of immunosuppressive medications. The advent of new biological agents has precipitated a further examination of the links between infection, the underlying disease and its treatment, resulting in several interesting observations. Interleukin-1 (IL-1) and tumour necrosis factor alpha (TNF-alpha), the major pro-inflammatory cytokines, play important roles in host defence against infection. Inhibition of their activity could therefore be anticipated to augment the risk of infection in patients with pre-existing abnormalities of immune regulation. Slight increases in the rates of infection were noted in the clinical trials of IL-1 receptor antagonist (IL-1Ra). In addition, a small number of opportunistic infections have been observed with the TNF inhibitor, etanercept. However, a marked increase in opportunistic infection, particularly tuberculosis, has occurred with the use of infliximab, an agent that also blocks TNF activity. The precise mechanisms by which these agents predispose to infection are currently being explored. The answers are likely to add significantly to our knowledge of how immune dysfunction contributes both to the pathophysiology of disease and the complications of therapy.