A concise assessment of the risks to human health posed by exposure to 1 1 1 2-tetrafluoro-ethane, a gaseous fluorocarbon used primarily as a refrigerant for high-temperature refrigerators, including domestic refrigerators and automobile air conditioners. Concerning environmental behavior, the report cites evidence that 1 1 1 2-tetrafluoroethane partitions almost exclusively to the atmosphere. Limited evidence suggests that the chemical does not accumulate in biota or adsorb to soil or sediment. The chemical's overall lifetime in the troposphere is estimated to be 14.6 years. Recent observations show a rapid increase in atmospheric concentrations, mainly as a result of emissions over the past decade. Modeling indicates insignificant ozone depletion potential, significant global warming potential, and negligible acidification potential. Data on toxic effects are limited. Animal studies have identified a reduction in maternal body weight gain in rabbits and signs of delayed fetal development in rats. Studies of carcinogenicity were judged to be inconclusive. Data on health effects in humans are limited to a single study conducted in volunteers. The study found no abnormalities following exposure via inhalation and no clinical signs of toxicity. The low toxicity of 1 1 1 2-tetrafluoroethane to the few aquatic organisms tested, as well as the chemical's high volatility, indicate that risks to aquatic organisms are negligible.