Field emission from carbon nanotubes can be affected by common carbon-containing residual gases in vacuum systems. In this article, we will show the effects of CO, CO2, CH4, and C2H4 gases on the field-emission currents of patterned multiwalled carbon-nanotube arrays prepared by chemical vapor deposition. Exposure to CO and CO2 at 10(-5) Pa can reduce the emission current from 22% to 49%, depending on the specific partial pressure and exposure time. Such a reduction can be fully recovered by continuous emission under a high vacuum of 10(-6) Pa. Exposure to CH4, and C2H4 can increase the current, but the current stability is poor, and after the exposure, the current did not recover. (C) 2003 American Vacuum Society.