For decades certain diseases, such as glomerulonephritis, polyarteritis nodosa, scleroderma and serum sickness, have been linked with autoimmune pathogenesis. During recent years a host of additional diseases traditionally thought to have some genetic predisposition but with obscure etiology have been suspected of being autoimmune in nature. Rheumatoid arthritis, diabetes, myasthenia gravis and thyroiditis are diseases of widely divergent organ systems, yet may well have common pathways of pathology via immune complexing mechanisms. Herein we present evidence supporting the concept that renal artery stenosis (occurring primarily in association with the middle aortic syndrome or after renal transplantation) is of immune etiology. Although the specific antigenic agent is still to be defined there is growing acceptance of the theory that medium and large vessels are subject to autoimmune vasculitis in many aspects similar to the autoimmune affections of small vessels. Several cases are presented. Some of these suggest an immune reaction by the natural history but without evidence of immunochemical reactants in the involved vessels, presumably because active disease was arrested at the time of study. In other cases immunofluorescent preparations demonstrate reactants in the walls of the vessels to document the hypothesis more convincingly.