Systolic left ventricular function was investigated by echocardiography in 23 young, type 1 diabetics and 11 control subjects. A stimulation by isoproterenol was performed in order to study beta-adrenergic cardiac responsiveness. M-mode recordings were digitized and analyzed by computer. Systolic parameters such as left ventricular fractional shortening and mean velocity of circumferential shortening were not different, but maximal velocity of shortening was increased both at rest (P less than 0.01) and with isoproterenol (P less than 0.05) in the diabetics. An abnormal systolic anterior motion of the mitral valve was found during administration of isoproterenol in 65% of the diabetics and in only one control. These findings are suggestive of a hyperkinetic state, associated with a poor metabolic control (high value of HbA1), together with adrenergic hypersensitivity in type 1 diabetes mellitus.