The photochemistry of several unreactive and moderately reactive nonmethane hydrocarbons (NMHC) in the background troposphere and stratosphere was investigated. A one-dimensional steady state model was employed to determine the vertical distributions of C//2H//6, C//2H//2, C//3H//8, C//4H//1//0, and C//5H//1//2. The impact of these species upon the tropospheric and stratospheric odd-hydrogen, odd-oxygen, chlorine, and carbon systems was studied for various possible free radical profiles and eddy diffusion coefficients. The results indicate that NMHC probably have only a small effect upon the background atmospheric photochemistry, although they might constitute a nonngeligible source of atmospheric CO. Also Cl atoms, in predicted present-day concentrations, comprise the major sink for stratospheric NMHC. Finally, if the chlorovinyl molecule (CHCl equals CH) were stable in the lower stratosphere, it would than be conceivable that C//2H//2 could be partially effective as a chain terminator to impede catalytic removal of stratospheric O//3 by Cl and ClO.