A study has been made of transmission at optical wavelengths through a hollow steel pipe the inner surface of which has a mirror finish. A suitable pipe has a bore of 1 in diameter to a tolerance of ±3 mil with a silver surface. It could carry a large number of communication channels, a typical pulse baseband width (for 10-mile spacing of regenerative repeaters) for each channel being 200 Mc/s, with an attenuation, allowing for bends of ½ mile radius, of 2½dB/mile. The mechanical requirements involve problems of construction which seem to be straightforward.