Regional lung function, using xenon 133-radiospirometry, and central hemodynamics were studied following normovolemic hemodilution with dextran 70. Normovolemic hemodilution to hermatocrit values of 25% increased cardiac output and pulmonary blood volume significantly. The systemic oxygen transport and mixed venous oxygen tension were unchanged. The acute hemodilution did not significantly change the distribution of ventilation or prefusion within the lungs. It is hypothesised that a tendency to an increase in arterial oxygenation is due to a reduced interstitial pressure in the basal region of the lungs, resulting from water absorption by the hyperoncotic dextran used for hemodilution.