In a prospective study, the clinical value of transoesophageal two-dimensional echocardiography (TOE) as compared with transthoracic two-dimensional echocardiography (TTE) was determined in patients with suspected infective endocarditis. Ninety-six patients were studied consecutively with an electronic sector scanner using 2.25 and 3.5 MHz probes for TTE and a 3.5 MHz probe embedded in tip of a flexible 12 mm gastroscope for TOE. Results of surgery and autopsy were available for 20 of the 96 patients with infective endocarditis and echocardiographically demonstrated vegetations and 70 control patients with valvular heart disease without infective endocarditis and no signs of vegetations, who were studied preoperatively with TTE and TOE. For TTE and TOE, the measured sensitivity was 63% and 100%, specificity 98% and 98%, positive predictive accuracy 92% and 95%, and negative predictive accuracy 91% and 100%, respectively. In 39 patients who had positive blood cultures, vegetations were found by TOE in 32 patients (82%), but in only 27 patients (69%) by TTE. Image quality was the main factor contributing to the superiority of TOE over TTE: it was reduced in 11/20 patients (55%) in whom vegetations were not detected by TTE. Another important factor was the size of vegetations. Only 6/24 vegetations (25%) of less than 5 mm but 9/13 vegetations of 6-10 mm, and 14/14 vegetations of greater than 11 mm detected by TOE were also observed with TTE. The clinical importance of detecting vegetations was demonstrated by the rate of embolism. In patients with vegetations embolism was 25% when blood cultures were positive and 21% when they were negative. In patients without echocardiographically detectable vegetations signs of embolism were seen in no patient with positive and 7% of the patients with negative blood cultures. Evidence of vegetations was found on the aortic valve in 14 patients and on the mitral valve in seven patients in whom valvular incompetence was not present, indicating that the valve had not yet been damaged significantly. TOE is superior to TTE in detecting vegetations in suspected infective endocarditis because of better image quality, particularly when vegetations are small. TOE seems to be indicated in patients with suspected endocarditis and reduced image quality or negative TTE results. Early detection of vegetations on valves may help confirm the diagnosis of infective endocarditis at an early stage and hopefully lead to an improved prognosis by reducing delay in instituting appropriate therapy.