The authors report two suicides that resulted from the intentional inhalation of automobile exhaust gases in which death occurred without the formation of physiologically significant amounts of carboxyhemoglobin. These circumstances are correlated with measurements of the involved vehicles' exhaust gases, which showed reduced concentrations of carbon monoxide present, reflecting improvements in automobile engine technology. In the absence of carbon monoxide toxicity, the authors attribute death in these cases to asphyxia caused by carbon dioxide intoxication and diminished atmospheric oxygen concentrations.