We examined the effects of altitude hypoxia on the subject's cognitive functions and psychological state. Two assessment approaches were used, a cognitive-motor task and a structured interview. An experimental group of six subjects was tested three times: once under conditions of normoxia, once 8-20 h after a rapid climb to an altitude of 4383 m, and once 48-60 h after ascent to that altitude. A comparison of the experimental group's performance on the cognitive-motor task with that of a control group showed a difference on the second administration: the experimental group's performance did not improve, whereas the control group's performance did. This difference recovered on the third administration. A comparison of the subjects' verbalizations during the three interviews showed that they experienced a strong crisis during the first period at altitude, which improved partially during the second period. Evidence for use of certain defense mechanisms, e.g. self-concern, was found 8-20 h after ascent; both dependent measures were adversely affected. These measures recovered after 48-60 h.