The prototype of a multiplanar transesophageal echocardiographic transducer was evaluated clinically. This 5 MHz, phased array, 64-element transducer allows to continuously rotate the imaging plane from the transverse (0-degrees) position to a maximal 180-degrees position, thus encompassing transverse, longitudinal, and every intermediate position. The transducer is incorporated in the echoscope tip measuring 16 by 11 by 40 mm. The shaft of the instrument is 110-cm long and has a 9-mm diameter. The instrument has pulsed wave, continuous wave, and color Doppler capabilities. 176 clinical patients were examined with the multiplane transducer. No complications occurred. Advantages of this transducer included: 1) comprehensive scanning of the whole mitral circumference and mitral valve; 2) quick and precise alignment of aortic valve long and short axis views, including long axis views of the ascending aorta, with a mean visualized length of 6 cm; 3) improved imaging and evaluation of transvalvular and paravalvular regurgitant jets in mitral and aortic valve prostheses; 4) complete evaluation of all left ventricular segments using multiple planes from transgastric and transesophageal transducer positions. An important potential application is three-dimensional reconstruction of cardiac structures and color Doppler jets.