Transesophageal echocardiography (TEE) was introduced recently in France. The aim of this study was to review the diagnostic value of this technique after 8 months' use in our cardiology department. A total of 532 TEE studies were carried out between April and December 1988 in 396 patients (average age 54 years, range 17 to 89 years) at Tenon Hospital. The failure rate was 1.8 per cent (N = 10), over half of which occurred at the beginning of the operator's experience. TEE was particularly valuable compared with the standard transthoracic approach in the following instances: the investigation of mitral stenosis, especially before percutaneous valvuloplasty (N = 75). A left atrial thrombus was demonstrated in 5 cases by TEE vs none by standard echocardiography. There was also a much higher diagnostic sensitivity for small interatrial shunts (40 vs 6) resulting from transseptal catheterisation. In the preoperative investigation of severe mitral regurgitation (N = 29). The etiology was accurately diagnosed in 29 vs 26 cases, and the mechanism of the regurgitation was correctly classified especially in cases of ruptured chordae (15 vs 6 cases). In endocarditis (N = 26) by the visualisation of abscess of the aortic ring (7 vs 1) and vegetations (19 vs 8). In prosthetic valve dysfunction (N = 65) by the demonstration of primary degeneration of bioprostheses (7 vs 4), perivalvular leaks (10 vs 4) and non-occlusive thrombi of mechanical prostheses (3 vs 0). In cases of intracardiac tumours, dissection of the thoracic aorta and atrial septal defects.(ABSTRACT TRUNCATED AT 250 WORDS)