Transesophageal echocardiography with color flow Doppler studies was performed on 10 consecutive patients who had right atrial masses identified by transthoracic echocardiography. In one patient with right atrial myxoma, transesophageal study identified the tumor by its attachment to the atrial septum and ruled out the transthoracic finding of possible additional tumor mass in the right ventricle. In two instances the mass in the atria were deemed to be thrombi because of lack of attachment to the atrial septum, atrial fibrillation, and enlarged right atrial chambers. In all patients, the thrombi appeared larger by transesophageal study and was associated in one instance with atrial septal defect. The atrial septal defect was not identified by the transthoracic study and probably accounted for stroke of the patient through paradoxical emboli. In six patients, because of superior quality images rendered by transesophageal imaging, the right atrial mass lesions were deemed to be anatomic variants, which included prominent eustachian valves, remnants of Chiari network, and thickened atrial septum. We concluded that transesophageal echocardiography is superior to transthoracic imaging in elucidating the cause and significance of right atrial mass lesions and that it helps in guiding appropriate therapy.