A consecutive series of 300 M-mode and two-dimensional echocardiograms was reviewed retrospectively by 2 independent observers. These tests had been performed in adult patients who were either ambulatory or hospitalized in a community hospital. The diagnostic contribution of two-dimensional echo in comparison to M-mode was nil in three-quarters of the cases; it was rated as important or essential in only 20% of the cases. It is concluded that M-mode echocardiography in adults retains its value in everyday cardiac practice.