The effect of oxygen inhalation on cutaneous thresholds for cold sensation wa s determined by exposing a 50 sq. cm area on the chest to a radiant cold source of variable intensity for 2 second intervals in 11 healthy 23 to 26 year old nude subjects at two ambient temperatures. Oxygen breathing produced a similar significant increase in cold thresholds in both cool 22.4to26.5C and warm 36.6to39.3C environments. Observations at warm ambient temperatures substantiate the oxygen effect independent of suspected reflex vasoconstriction in the cool environment. These experiments confirm the cold threshold raising effect of oxygen inhalation and emphasize the danger of relying solely on physical calculations of the intensity of a thermal stimulus. Indirect evidence that oxygen inhalation hinders carbon dioxide transport continues to accumulate. Instrumentation analyses suggest methods for improving polarographic measurements for po2 and for the infrared carbon dioxide analyzer.