We investigated the impact of extracorporeal shock wave lithotripsy on cardiac pacemakers, arterial calcifications, and vascular clips. When 22 cardiac pacemaker pulse generators mounted five cm. lateral to the focus of the lithotripter were subjected to both synchronous and asynchronous shock waves, one reverted to magnet rate with synchronous shocks and 11 were inhibited by asynchronous shocks. None was damaged or spuriously reprogrammed. In a second experiment, 10 canine and cadaveric aortas and common iliac arteries with metal surgical clips on two to three mm. branches were pressurized with methylene blue in normal saline at 150 mm. Hg and fixed in the Dornier lithotripter. Shock waves (N = 2000; 22 kV) were focused on the surgical clips and no leakage of methylene blue was found.