In a 7-d dry immersion experiment normal volunteers were given meals prepared with account of personal body mass and caloric demand. Water, salt and calcium consumption with foods and beverages was calculated. The bath water was controlled within the range of comfortable temperatures. Investigated were osmoregulation and renal excretory function, circulating plasma volumes, and O2 transport by erythrocytes. Besides, functional state of cutaneous microcirculation was assessed using the laser-Doppler-iontophoresis in vivo with acetylcholine and nitroprusside. Dry immersion consistently accelerated excretion of liquid and electrolytes (sodium) and reduced the volume of circulating plasma (VCP, determined from hematocrit) together with relative hyperhemoglobinemia and hypererythrocitemia at the beginning of immersion. During the first week of recovery VCP showed a relative increase w/o change in specific hemoglobin content. Immersion affected the skin vessels reaction to acetylcholine which depends on prostaglandins production by endothelial cells but not NO-dependent vasodilation. Consequently, limitation of physical activity by itself causes endothelium dysfunction for the reason of slackening the shift voltage force and resulting in endotheliocytes dysfunction and, probably, in activation of apoptosis.