Abstract: The total flavone glycoside of Oxytropis falcata, benadryl, sodium pentobarbital and aminophylline were studied in high altitude and hypobaric conditions to assess the acute toxicity in mice. It was found a tendency that the toxicity was increased with altitude. But the difference was insignificant in 2270 m compared with sea level. While the altitude "rose" from 3500 to 7000 m a significant increase of the acute toxicity occurred accor-ding to the feature of drugs themselves. The aminophylline was more toxic with altit-udes, in 3500 m the dosage of LD₅₀ decreased 14.5%, decreased 20.2% and 28.5% in 5000 m and 7000 m respectively. The degree of decreased LD₅₀ with altitudes was in the order of aminophylline, sodium pentobarbital, benadryl and the total flavone glyco-side of Oxytropis falcata. It is thought that hypoxia can be one of the factors to inf-luence acute toxicity of drugs; thus, enhanced toxicity may be attendant to high altitude medicine.