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 C2H6, C2H2, C3H8, C4H10, and C5H12. 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. Our results indicate that NMHC probably have only a small effect upon the background atmospheric photochemistry, although they might constitute a nonnegligible 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=CH) were stable in the lower stratosphere, it would then be conceivable that C2H2 could be partially effective as a chain terminator to impede catalytic removal of stratospheric O3 by Cl ClO.