The present study investigated whether nitrous oxide (N2O) attenuates shivering thermogenesis during cold water immersion in a dose-dependent manner. Seven male subjects were immersed to the neck for 60 min in 20 degrees C water on five separate occasions while breathing either air (AIR) or a normoxic mixture of 10, 15, 20, or 25% N2O balanced with N2. All N2O concentrations investigated caused a significant (P < 0.02) reduction in shivering thermogenesis compared with AIR. Despite similar heat flux from the skin, the relative changes in esophageal temperature from resting preimmersion levels were significantly greater (P < 0.05) during the N2O trials compared with AIR, with no significant difference among the N2O conditions. A dose-dependent trend in the perception of thermal comfort was observed for the N2O conditions. It is concluded that shivering thermogenesis, and thus thermal balance, is affected to the same degree for the range of inspired N2O concentrations investigated, with no discernable dose-dependent effect.