A discourse analysis was carried out on nine European lowlanders during a 2-month scientific expedition at high altitude including a 3-week stay in extreme survival conditions at the summit of Mt. Sajama (6542 m), in order to contribute to the understanding of psychological adaptation to extreme environments. This discourse analysis was part of a wide-ranging scientific investigation involving 12 scientific and medical research protocols which targeted human adaptation to high altitude chronic hypoxia. The objective of this study is to better understand the presence of linguistic markers capable of translating the subject's psychological state when faced with a threatening environment. This study was based on a method of propositional speech analysis developed by Ghiglione and Blanchet which emphasizes the cognitive function of verb categories, modalizers and adjuncts used by subjects. The method was developed in conjunction with psychopathological studies of the depressive state. Speech was recorded at time T1, 4 days after reaching the summit of Mt Sajama, and at time T2, 2 days before descending the mountain peak. These results revealed that in the absence of depression in any psychopathological sense of the word, normal subjects would react to their environment with a depressive component. However, the results of this study equally illustrate for some subjects a correspondence between those states with a depressive component and a physiological incomplete adaptation to high altitude. This correspondence could reflect the pathogenic effect of an adaptation deficit or could be in keeping with the literature concerning an incomplete adaptation effect induced by a latent depressive state.