Laser-assisted lithotripsy is a minimally-invasive method for destroying or disruption of human urinary stones. For this purpose laser light delivered through the flexible sealed waveguide or fibre could be utilized. On the output end of the delivery system the laser ligth is focused onto the surface of urinary stones with various size and various composition. In clinical urological practise the Ho:YAG laser with the generated wavelength 2100 nm operated in free-running regime is commonly used. The aim of our investigation was to compare the damage effects of Ho:YAG laser radiation with the promissing Er:YAG laser radiation. The Er:YAG laser generates radiation with the wavelength 2940 nm, which coincides with the local absorption maximum of water. We have compared the laser effect with the help of uniformly produced model samples made from special plaster. The size of the samples was 10x10x10 mm. The perforation and disruption effectiveness of Ho:YAG and Er:YAG laser radiations were performed and compared. In the final step the laser lithotripsy of human urinary stones was tested with Er:YAG laser radiation delivered through the special COP/Ag hollow waveguides sealed with fused silica cap.