The measurement of cardiac output by electrical impedance plethysmography (non invasive technic) seems to be attractive but is still the subject of a certain number of critics. The authors have tried to compare it with a method which validity is well documented, the thermodilution. By these two methods, 87 measures of cardiac output have been performed in 14 hospitalized patients in intensive care, attained of various affections but exempts of cardiac or pulmonary lesions and in stable hemodynamic state. The stroke volume measured by electrical impedance plethysmography is calculated using Kubicek's formula: SV = Q (L2/Zo2) (dz/dt min) t. Results were as follows: absence of significative difference between the coefficients of variation of each series of measures (coefficient of mean variation, 5,6 +/- 3,4 p. cent for impedance and 3,8 +/- 3,2 p. cent for thermodilution); absence of significative difference between the mean values of cardiac output (7,59 +/- 2,69 l . min-1 for impedance and 7,72 +/- 1,99 l . min-1 for thermodilution); highly significant correlation between values for cardiac output obtained for each of these two methods )r = 0,804; n = 87; p less than 0,001). The authors conclude that in patients in intensive care whose pulmonary or cardiovascular system is not in critical situation, the electrical impedance plethysmography appear as a secure method for cardiac output measurement. However its generalisation still require other works.