Experimental animal [rabbit, rat, other lab animals] research was used to compare the coagulatory qualities of the Ar laser and the neodymium-YAG [yttrium-aluminum-garnet] laser to results obtained through electrocoagulation. The Ar laser effects a necrosis near the urinary bladder wall surface, and when the energy density is increased, it may ablate the tissue to the point of perforation. The neodymium-YAG laser effects a bandshaped necrosis that penetrates all layers of the urinary bladder wall without primarily resulting in an ablation of tissue. Electrocoagulation results in irregularly demarcated necroses of varying depths, which can be explained by the uncontrolled flow of the high-frequency currents according to the paths of least resistance. The neodymium-YAG laser is the one most suited for transmural coagulation of defined areas within the urinary bladder wall due to the even spread of its thermal energy that is independent of the affected tissue structures, and to its deep coagulatory qualities which in turn are due to the laser''s minimal tissue absorption. The neodymium-YAG laser allows the setting of reproducible, sharply demarcated necroses into the bladder wall with an ensuing complete destruction of all wall layers. The wall framework within the necrotic area remains intact, so that the danger of perforation is kept at a minimum.