Echocardiographic measurements of minor axis and wall thickness and calculations from these two measurements of left ventricular end-diastolic volume and mass were performed in 24 patients and compared with angiocardiographic measurements of the same variables in corresponding patients. The echo-measured left ventricular end-diastolic chamber dimension (Dd) correlated closely with the angiographic minor axis in the AP plane (correlation coefficient 0.87 and SE ± 0.45 cm) and with the minor axis from the lateral film (r = 0.91, SE ±0.39 cm). Similar correlations were found between measurements by these methods of wall thickness (r = 0.89, SE ±1.3 mm), of end-diastolic volume (r = 0.94, SE ±30.6 cc), and of left ventricular mass (r = 0.88, SE ±49.19 g). The reproducibility of this method was established by independent recordings and measurements of echo Polaroid films by two observers. The percent systolic wall thickening, as determined by echocardiography, identified subjects with ejection fractions greater or less than 0.50. Echocardiography offers a reliable and reproducible method for measuring left ventricular wall thickness and mass. Finally, ultrasound may provide an accurate method for measuring systolic wall thickening in man.