Due to the decreasing partial pressure of oxygen, high altitude sickness can occur at heights over 2,500 m. This can be best avoided by slow adaptation to the altitude (acclimatization). In this way the organism adapts to the chronic hyperventilation and in the further process the oxygen content is normalized by an increase in erythrocytes. The commonest form of high altitude sickness is acute mountain sickness which is characterized by the leading symptom of headache. When additional signs of ataxia occur there is an acute danger of edema which is associated with a high mortality. Stress dyspnea, coughing and rasping breathing noises also occur by the potentially fatal high altitude pulmonary edema. All forms of high altitude sickness can be countered by a rapid descent to a height of at least 500 m. In acute mountain sickness acetazolamide can be administered (2 × 250 mg), for high altitude cerebral edema dexamethasone (3 × 4-8 mg) and for high altitude pulmonary edema nifedipine (initially 10 mg then 20 mg retard).