The acute effects of extracorporeal shock waves on renal morphology were studied by light and electron microscopy in 14 dogs. One kidney received an average clinical number of exposures, the nonexposed, contralateral kidney serving as control. The original Dornier HM-3 generator was used in 3 animals, the modified version in 11. Intravascular radiographic contrast medium was administered in five animals. Damage was observed in all exposed kidneys, none in the contralateral control kidney. The effects were characterized by renal and perirenal hemorrhage and edema, parenchymal hemorrhagic foci with tissue destruction, often extending from cortex to medulla. In the nearby regions there was endothelial cell damage in arteries, veins and glomerular capillaries. Breaks in the wall of these vessels were detected with platelet plug formations and thrombi. In glomeruli, breaks of Bowman's capsule and epithelial cell damage with loss of foot processes were observed. A wide range of tubular cell damage was demonstrated, ranging from vacuolization to complete necrosis. Tubular lumina were filled with red cells, indicating renal origin of hematuria. The tissue damage was less pronounced in kidneys exposed to the modified lithotriptor than to the original. No difference in the quantity or quality of damage was detected whether radiographic contrast medium was administered or not.