Optical fibers fabricated from silver halide crystals (AgCl1Br1.I)are transparent in the far infrared (3-15 μrn). The) can transmit CO. laser radiation with power densities greater than 3 × 104 W/cm2 in the CW mode or short pulses with power densities on the order of 5 × 106 W/cm2. A laser catheter system based on a silver halide fiber and a pulsed CO, laser was used to perform laser angioplasty and atrial septostomy in vivo. A similar system was used to eo-aguiate bleeding gastric ulcers in vivo. Silver halide fibers were also - used in diagnostic procedures, such as noncontact temperature measurements during laser surgery and hyperthermia cancer treatment.