The interaction of NH3 and NO2 with heterogeneous bundles of carbon single-walled nanotubes (SWNTs) has been studied using FTIR spectroscopy and temperature-programmed desorption (TPD). Both NH3 and NO2 adsorb at room temperature, and the interaction results in strong shifts of the vibrational modes of the molecules relative to the gas phase. The data suggest that NH3 adsorbs via both its lone pair and its H atoms. NO2 adsorbs in an asymmetric configuration via at least one of the oxygen atoms. Analysis of the IR data suggests that these molecules adsorb by interacting with multiple nanotubes within a bundle of SWNTs. Additionally, trimethylamine, a compound similar to NH3, does not adsorb at room temperature. It is postulated that the size of trimethylamine prevents it from entering the grooves between nanotubes in the sample, whereas NH3 and NO2 are small enough to enter the grooves and interact with multiple nanotubes.