Following reports of hemorrhage from renal microaneurysms caused by renal biopsy, renal arteriography has been used increasingly as a screening procedure prior to renal biopsy as well as for diagnostic investigation. The incidence of renal microaneurysms has been documented in a group of 40 cases of suspected polyarteritis nodosa, of whom 15 were confirmed, and only 2 had microaneurysms. Both subjects with microaneurysms had more florid clinical disease. In view of the low incidence of microaneurysms it is suggested that renal angiography should be used as a diagnostic investigation only in cases with florid clinical disease and not as a screening procedure prior to renal biopsy.