Field emission of carbon nanotubes (CNTs) grown on carbon cloth under various growth conditions has been studied. Iron sulfate or stainless steel was used as the catalyst, acetylene (C2H2) or methane (CH4) was used as the carbon source, and argon (Ar), hydrogen (H-2), or ammonia (NH3) was used as the carrier gas. It is found that the morphology of CNTs is strongly dependent on the growth conditions: temperature, gas combination, and growth time. In general, higher temperature produces better field emitters than lower temperature, C2H2/Ar is better than C2H2/NH3, but CH4/H-2 is the best, and longer growth time normally yields longer CNTs leading to better field emitters. The best sample was made from 0.18 mol/l iron sulfate catalyst with CH4/H-2 at 860 degrees C for 2 h: an emission current density of 1 mA/cm(2) was obtained at 0.4 V/mu m corresponding to a field enhancement factor of 3.5 X 10(4). (c) 2005 American Vacuum Society.