In a prospective study, 44 children receiving Adriamycin (ADR) for various neoplastic diseases underwent serial estimations of the systolic time intervals (STI) for the noninvasive assessment of left ventricular myocardial performance. Five of the 44 children developed clinical signs of ADR-related congestive heart failure at a cumulative dose of less than 550 mg/m2 body surface area. Clinical symptoms, changes in the electrocardiogram and in the chest X-ray were preceded in every case by changes of the STI, mainly a prolongation of the left ventricular pre-ejection period (PEP), or a decrease of the ejection time (ET)/pre-ejection period (PEP) ratio (ET/PEP). A continous increase of the PEP and a decrease of the ET/PEP-ratio also gave an indication of myocardial dysfunction during ADR treatment in the other children without clinical signs of congestive heart failure. This subclinical cardiotoxic effect of ADR below the critical cumulative dose of 550 mg/m2 was observed in children with pre-existent myocardial damage, with preceding thoracic irradiation, or during concurrent chemotherapy, of which cyclophosphamide seemed to be most important. Thus, the estimation of the STI proved helpful and reliable in the early detection of incipient heart failure and in the selection of high risk patients in children receiving ADR treatment.