The aim of this study is to compare the performance of Transesophageal Echocardiography (TEE) and the Transthoracic approach (TTE) in the diagnosis of Infectious Endocarditis (IE). Between October/90, the data we started transesophageal ultrasound, till April/92, we performed 33 TTE in inpatients with clinical suspicion of IE. Twenty pts (61%) had one or two prosthesis. All the pts had a previous TTE. The diagnosis of IE determined by non-echocardiographic data was established on 18 pts. The other 15 pts, without clinical criteria of IE, were used as the control group. The Echocardiographic criteria for the diagnosis of IE were for both diagnostic tools the presence of masses suggesting vegetation of abscess. The diagnosis was correctly made by TTE in 8 of the 18 pts (S-44%) and by TEE in 16 of the 18 pts (S-89%) with clinical criteria for IE. Of the 15 patients without clinical criteria for IE 14 were correctly identified by TTE (Sp-93%) and 13 by TEE (Sp-89%). With a similar VPP (89%) for both tools has TEE a significative higher value for NPV than TTE (87% vs 58%). This study suggests that TEE, at a same level of specificity as TTE, is highly more sensitive in the diagnosis of IE (S-89 14 for TEE and S-44 23 for TTE) a figure that recommends that all patients with clinical suspicion of IE and a negative TTE should perform a TEE.