Three-dimensional echocardiography is a new imaging technique that allows more realistic visualization of cardiac morphology. This study presents data about the diagnostic potentials of this technique concerning cardiac mass lesions, as well as its feasibility in clinical application. After the conventional investigation, multiple cross-sectional images were obtained during automatic forward advancement of a monoplane transducer mounted on a transesophageal probe. Three-dimensional reconstruction and volume determination were performed off line. Twenty-four patients were studied. In 14 cases results of echocardiographic computed tomography (echo-CT) were compared with those of monoplane/biplane transesophageal echocardiography. In 23 patients a conventional transesophageal investigation with the echo-CT probe and in 20 patients tomographic scanning were possible. Data acquisition required 12 +/- 4 minutes and three-dimensional reconstruction required 35 +/- 14 minutes. In 13 patients mass lesions were found; in 11 of 13 patients echo-CT provided diagnostic information about the precise spatial orientation and morphology of cardiac structures that could not be obtained by monoplane/biplane transesophageal echocardiography. The technique revealed accurate distance measurements and volume determination of mass lesions. Echo-CT is a further step toward the application of clinically useful three-dimensional echocardiography.