The authors have investigated in 10 young and healthy men the changes occurring in the cardio-respiratory apparatus following the perfusion with non-colloid isotonie volemic solutions. Exploration of volumetry and of pulmonary mechanics have been performed, hemodynamic tests and pulmonary angiograms. The results indicate the development of slight interstitial oedema, without intra-alveolar transsudation or obstructive phenomena in the aerial pathways. The cardio-vascular apparatus shows satisfactory adaptability through central and peripheral mechanisms in conditions of hyperhydration.