Renal circulation following 3 to 14 min of cardiac arrest was investigated in 21 mongrel dogs by angiography, microangiography and histology. Arrest longer than 7 min caused variable degrees of abnormal angiographic findings after resuscitation: (1) segmental perfusion defects and cortical areas without nephrographic effect, (2) loss of demarcation of cortex and medulla, (3) decreased nephrography, (4) faint and delayed filling of the renal veins, (5) diffuse segmental spasm of the interlobar arteries with delayed emptying. Microangiography demonstrated non-filling of glomeruli in segmental areas of renal cortex, diffuse malperfusion and vasoconstriction as well as obliteration of afferent arterioles due to red blood cell aggregation. No tendency toward recovery within the 5-hour resuscitation period.