This is a rare, but potentially very troublesome disorder. We have been able to carry out detailed radiological, histological and biochemical investigations on 51 patients and the results of these investigations are presented. Considerable evidence of abnormal platelet activity has been found. The histological evidence has come from both biopsy and nephrectomy specimens and has shown aggressive atherosis leading to microembolic lesions and in some cases showing microaneurysm formation. In some instances this has led to areas of infarction both small and large. Most of the cases studied have been fully followed up and it has been found that despite the histological changes, the blood pressure remains normal and no demonstrable deterioration in renal function occurs. Attempts at treatment are described and discussed.