In the Eastern Alps, the Dachstein massif with a height of almost 3000 m is an ideal location for investigating the effects of changes in altitude on the human body. A cable car allows an ascent within a few minutes to 2700 m, where the partial pressure of oxygen is about 550 mm of mercury compared to 760 mm at sea level. Ten healthy subjects performed a reaction time task at an altitude of 990 m and 2700 m. The subjects were instructed to perform a right hand index finger movement as fast as possible after a green light had flashed. The green light flashed 50 times. Simultaneously to the task, the electroencephalogram (EEG) was recorded. The event-related desynchronization (ERD) analysis of the EEG data showed that changes in alpha ERD values are not significant, but event-related synchronization (ERS) values in the beta band decrease significantly from around 50 % to 10 %. Furthermore, the mean frequency of the beta band increased from 16.68 Hz to 16.81 Hz (p = 0.0019) with the ascent. The suppressed post-movement beta ERS at an altitude of 2700 m may therefore be interpreted as a result of an increased cortical excitability level when compared with the reference altitude of 990 m above sea level.