Fifty consecutive patients (mean age 56 years) were examined to evaluate the reliability of transesophageal echocardiography in the evaluation of the left proximal coronary artery. Results of 28 cases were compared to selective coronary angiography. Echocardiography was able to visualize the left main artery for the length of 1.0 +/- 0.6 cm in all patients (100%), the left circumflex artery for maximal 3.1 +/- 1.4 cm in 86% and the left anterior descending artery as long as 2.3 +/- 0.9 cm in 58%. The intraluminal diameter of the most proximal localized segments measured by echocardiography and angiography in the LAO and RAO-projection was in terms of the left main artery 4.1 +/- 0.9 mm, 4.1 +/- 0.9 mm and 4.0 +/- 0.9 mm (n.s.), of the left circumflex artery 2.8 +/- 0.5 mm, 3.3 +/- 0.8 mm and 3.3 +/- 0.9 mm (n.s.) and of the left anterior descending artery 3.0 +/- 0.8 mm, 3.4 +/- 0.7 mm, and 3.6 +/- 1.0 mm (n.s.). In respect of detection of coronary artery stenoses in correspondence to the coronary angiogram sensitivity was 81%, specificity 93% and positive predictive accuracy 86%. Quantitative analyses of the coronary anatomy and the correlation to angiography could contribute to the validation of transoesophageal echocardiography.