The effects of single 1-hour immobilization stress exposure and of long-term (40 days) adaptation to intermittent high altitude hypoxia (in hypobaric chamber at "altitude" 4000 m, 4 hr, a day) on serum myoglobin content were studied in Wistar rats. It has been shown that such stress exposure induced the 2.5 fold increase in the serum myoglobin content. The adaptation did not change the myoglobin content, but effectively limited mentioned above stress-induced increase in the serum myoglobin level. These data suggest that serum myoglobin content can be used as a criterion for stress damage and efficiency of factors protecting against stress damage.