Twelve patients with chronic cor pulmonale due to chronic obstructive pulmonary disease have been examined with 2D echocardiography, performing four-chamber view by apical and subcostal approaches, and the right ventricular outflow tract view by the subcostal approach. These views have permitted evaluation of right ventricular volumes, and hence right ventricular ejection fraction, by the use of three different geometrical formulae: the biplane area-length method, Simpson's rule and the pyramidal method. The ejection fraction values obtained from each method have been compared to those obtained by equilibrium radionuclide angiocardiography. Four-chamber apical and subcostal views were satisfactorily recorded in 10 of the 12 patients (83.3%), and right ventricular outflow tract view in 8 patients (66.6%). No significant statistical differences have been found between measurements obtained from the three different echocardiographic examinations performed on each subject by the same operator, so demonstrating a satisfactory reproducibility of the technique. The highest correlation coefficient for ejection fraction was shown by Simpson's rule (r = 0.96, p less than 0.001), with a very narrow confidence intervals, while the r values for the biplane area-length method was 0.63 (p less than 0.05) and for the pyramidal method 0.50 (not statistically significant), with increasingly wider confidence intervals. The statistically significant difference between the three correlation coefficients demonstrates the higher accuracy of Simpson's rule for the determination of right ventricular ejection fraction.