Atmospheric gas samples (0.1m3) were collected at ground level during January/February 1984 in Las Vegas, Nevada for 14C/13C accelerator mass spectrometry and total abundance measurements of CO and CH4. During winter months in this locale, CO concentrations can occur at 10 to 100 times background, occasionally exceeding the National Ambient Air Quality Standard (NAAQS). Methane concentrations show a slight enhancement (∼24%) above the background (non-urban troposphere) level. A comparison of CO and CH4 concentrations shows a good linear correlation which may indicate a common source. Preliminary 14C/13C results of the two species suggest that fossil emissions are the predominant source of excess CO and CH4 in the samples taken. Estimates of anthropogenic CO and CH4 are important for source apportionment of combustion emissions. In addition, this information is valuable for understanding the global CO and CH4 cycles and, therefore, human impact on climate and the stratospheric ozone layer.