Wistar rats underwent moderate hypoxia by exposing them to a respiratory gas mixture containing 7% oxygen, for 30 min. The myelin was analyzed at 4 h 24 h, day 14, and day 60 after hypoxia. The group of neutral lipids isolated from myelin was analyzed by GC-MS (gas chromatography-mass spectrometry) to separate and measure free sterols. In the myelin of hypoxia treated animals the pattern of free sterols was variable. Cholesterol concentration decreased with the changes in the content and composition of sterols present in smaller amounts. These changes may indicate the disturbances in some steps of cholesterol biosynthesis and metabolism in pathologic conditions. The appearance of sterols characteristic for plants (beta-sitosterol) was noticed in myelin of experimental animals. The possible reason for the presence of this sterol in animals may be the result of its intake during feeding, however, biosynthesis can not be excluded.