During the performance of routine angiography inpatients, 3 different forms of renal arterial spasm were encountered. Renal artery spasm may involve either large or small arteries of the kidneys. The temporary nature of the spasms may be demonstrated by additional angiography which shows no defect. Either a sufficient waiting period for the spasm to relent or the employment of a vasodilating drug through the catheter will usually suffice for this demonstration. Differentiation of spasm from fixed, organic disease is essential to prevent diagnostic error and improper therapy.