Mats and ribbons of well-purified single-wall carbon nanotubes have pronounced optical activity. The effect has been explained by formation of a crystalline structure of the material which was confirmed by high resolution electron microscopy and electron diffraction. Carbon microtubes also have optical activity effect caused by reflection of the light from the smooth wall of the tube close to the Brewster angle. (C) 2003 Elsevier B.V. All rights reserved.