Multiplane transesophageal echocardiography is a new development in transducer technology, which allows by rotation of the transducer to obtain not only transverse and longitudinal planes but also all intermediate planes. Exterior control allows continuous rotation of the scanning plane from the conventional transverse plane, corresponding to 0 degree, to the longitudinal plane, corresponding to 90 degrees and further to a left-right inverted transverse plane, corresponding to 180 degrees. Although the echoscope tip, which houses the rotatable transducer, is slightly larger than conventional probes, in our clinical experience of well over 400 cases, intubation of the esophagus is not more difficult than with the mono- or biplane probe. In comparison with the biplane technique the adjustment of intermediate planes is easier and less unpleasant for the patient, since mechanical irritation due to sideward flexion of the probe is less often necessary. Plane rotation, effected by control buttons in the echoscope handle, takes eight seconds from 0 degree to 180 degrees. The probe incorporates a 5 MHz phased array transducer, which alternatively works at 3.7 MHz. Pulsed, continuous and color Doppler are also integrated. Multiplane transesophageal echocardiography was used to investigate several clinical questions. In 41 patients with aortic valve stenosis the valve area was determined by planimetry. The valve area was measured in an individually aligned short axis view (between 50 degrees and 70 degrees). A high correlation (r = 0.95; Y = 0.9 X + 0.1; p < 0.01) with invasively determined valve areas by the Gorlin formula was found.(ABSTRACT TRUNCATED AT 250 WORDS)