After reviewing data from the literature concerning the effects of normovolaemic haemodilution on cardiac output and regional flow rates, the authors illustrate these concepts by a personal study involving the haemodynamics of 10 subjects undergoing operation in normovolaemic haemodilution. Removal of blood was compensated simultaneously by modified liquid gelatin in electrolytic solution (Plasmion) until the haematocrit was 0.30. Measurements were performed before haemodilution in patients in a steady state (anaesthetised, intubated, normoventilated), at the end of haemodilution, at the end of the operation, then 4 hours after recovery. There was no variation in blood pressure and heart rate, showing that normovolaemia was maintained. At the end of haemodilution, cardiac index increased from 3.10 to 3.84 l.min-1.m-2 (0.0517 to 0.0638 l.s-1 . m-2) (p < 0.005); stroke volume increased from 70 to 83 ml (p < 0.005); systemic resistance fell from 1585 to 1262 dynes. s.cm-5 (158.5 to 130.4 kPa.s.l-1) (p < 0.005); arterial oxygen content decreased from 191.1 to 152.1 ml.100 ml-1 (8.535 to 6.793 mmol.l-1) (p < 0.005), whilst oxygen transport was unchanged. These various haemodynamic measurements showed no significant changes at the subsequent times when they were measured, values remaining close to those obtained at the end of haemodilution. The results confirm the fact that norvolaemic haemodilution is accompanied by a fall in systemic vascular resistance with an increase in cardiac output. Regional circulations are thus improved. Since oxygen transport is unaffected, the oxygenation of peripheral tissues is ensured normally.