The method of hydrogen clearance was used in experiments on anesthetized cats for studying changes in the blood flow in the brain, kidneys and vena cava caudalis under prolonged antiorthostatism (45 degrees) and medication with caffeine and sidnofen. Specific features of the organ blood flow redistribution under the influence of antiorthostatism and the drugs administered before and after placement of the animals in the antiorthostatic position were established.