A discussion is presented of a modification to the molecular absorption band models in the LOWTRAN code for the uniformly mixed (N 20, CH4, CO, 02, and CO2) and the trace (NO, NO2, NH3, and SO2) gases. The transmission function adopted for each model consists of a double exponential defined by three absorber parameters and a single spectral parameter. All the parameters were determined optimally through a numerical procedure that incorporates line-by-line and measured transmittance spectra. Vertical concentration profiles are provided for these gases that may be used together with the 33-levels standard atmospheres in the calculation of slant-path transmittances. The present single model for the uniformly mixed gases in LOWTRAN is compared with the combination of the proposed individual models.