Eighteen patients with Wegener's granulomatosis with renal involvement have been studied. Their course before treatment has indicated how the disease may progress and has provided a framework for diagnosis based on clinical and radiological features combined with available histology. The need for such diagnostic criteria is emphasised by the fact that a firm histopathological diagnosis could only be made in nine patients. A strong association between Wegener's granulomatosis and previous suppurative or tuberculous respiratory infection has been noted as well as between intercurrent infection and relapse. Evidence that immune complexes play a pathogenetic role has come from the association between active disease and circulating immune complexes. The observation of a reversible abnormality of splenic clearance of altered red cells suggests that immune complex handling by the spleen is defective. Treatment of these patients has shown a surprising degree of reversibility in many manifestations, especially renal failure. Remissions occurring spontaneously or induced by steroids alone are temporary and steroids, if used alone, may adversely affect outcome. While confirming the central role of cyclophosphamide in the induction of remission, this study has indicated that its combination with steroids and/or plasma exchange may be valuable in initial control of fulminating disease. The fact that seven patients died during induction (as well as a further four in the succeeding five years) reflects the advanced disease at presentation and the infective problems associated with immunosuppressive therapy. This highlights the need for earlier diagnosis.