Sixteen boys with Duchenne muscular dystrophy (DMD) underwent serial investigations of echocardiographic left ventricular dimensions, systolic time intervals (STI), ECG and vectorcardiography (VCG). Spirometry with measurement of vital capacity and forced expiratory volume was also performed, as well as tests of muscle function. ECG was abnormal with high right precordial R-amplitudes even in the youngest patients. In contrast, VCG QRS area progressively diminished with age. STI and echocardiographic contractility indices decreased with increasing age. There was no clinically useful relationship between the various non-invasive variables on the one hand and results from skeletal muscle tests or lung function tests on the other, or between the different cardiac investigation methods. It is concluded that several non-invasive tests are needed during follow-up studies of Duchenne patients to evaluate the effects of treatment or assess prognosis.