Infrared-transmitting silver halide fibers, 0.3 to 1 .0 mm in diameter, were fabricated by extrusion and were found to have losses of about 1 dB/m at X = 10.6 Am. Infrared heterodyne experiments have been carried out using these fibers. Two stabilized CO2 lasers, of frequencies col and cwt, were used. The two laser beams were coupled into a single infrared fiber, using a Y coupler, with no other optics. Both beams were transmitted through this fiber to a fast IR detector. A heterodyne signal at a beat frequency cal - (02 was obtained from the detector.