We report on STM measurements of suspended carbon nanotubes at room temperature. We have found that the substrate-nanotube interactions influence the electronic proper-ties. Bands on supported tubes are shifted toward higher energies, while those on unsupported tubes are symmetric around the Fermi level. We have also observed that interference pattern of electron waves, caused by scattering on defects and edges, is more pronounced on suspended nanotubes. These results highlight the role of substrate interactions and shed some light on their influences on nanotube devices. (C) 2004 Elsevier B.V. All rights reserved.