Fiber-guided ablation of soft tissue with pulsed holmium and thulium lasers was investigated for intraluminal incisions. A bare fiber/tissue-contact application system with a nearly tangential irradiation geometry was first used in vitro on porcine ureter tissue. The efficiency and precision of the method was analyzed for different laser and application parameters. The ablation dynamics in water and tissue was investigated by fast flash photography. Uniform cuts could be achieved with 200- and 318-μm fibers using a free-running holmium laser with a pulse repetition rate of 10 Hz and an average power of up to 4 W. The depth of the cuts could be increased by using a thulium laser with the same laser parameters. By reducing the pulse duration by one order of magnitude, the quality of the incisions was made more irregular, the zone of thermomechanical damage increased, and the cuts became deeper owing to the growing influence of cavitation on shorter laser pulse durations. In a first clinical trial, 20 patients underwent holmium laser therapy to reopen ureteral strictures. Neither bleeding nor other adverse effects due to the laser treatment occurred, showing IR laser ureterotomy to be a suitable and promising minimally invasive technique. © 1998 Society of Photo-Optical Instrumentation Engineers.