Acute hypobaric hypoxia in rats (260 mm Hg., 90 min) was accompanied by a greater liver lysosomes osmotic susceptibility and by an increase in the relative content of the lysosomal enzymes (acid RNAase and acid phosphatase) in the nuclear fraction. This indicates an enrichment of the liver cell lysosomes with secondary lysosomes. No significant signs of labilization of the liver lysosomes were found. The adaptation of rats to hypoxia, as well as administration of the antihypoxant guthimin or of 1,4-bis-(3'-morpholinopropin-1'-yl-1') benzene hinder these changes to occur in the liver lysosomes during the organism reaction to hypoxia. But the effect of stabilization of the lysosomal membranes in a minor component in the antihypoxia action of the treatment.