The value of pre-treatment echocardiography has been assessed in 82 patients with small cell lung cancer (SCLC) presenting to one institution between 1985 and 1988. Thirty-six patients (44%) had echocardiographic abnormalities and 23 (28%) had abnormalities which had not been recognized at the initial clinical assessment. The most frequent abnormality was the presence of a pericardial effusion in 21 patients (26%). There was a strong association between the presence of a pericardial effusion and the clinical features of superior vena caval obstruction and pleural involvement. Non tumour-related cardiac abnormalities included significant left ventricular dysfunction (13 patients), valvular abnormalities (7 patients), left ventricular hypertrophy (8 patients). In 23 patients the echocardiographic findings caused us to change our treatment approach. In particular, 3 patients with incipient cardiac tamponade had urgent pericardiocentesis; doxorubicin was eliminated from the chemotherapy regimen in 19 patients with significant left ventricular or valvular dysfunction; and cis-platinum was not given to the 4 patients (including those with incipient tamponade) with large pericardial effusions because of potential problems with fluid loading. Three of five patients who developed treatment-related cardiotoxicity had abnormal pre-treatment echocardiograms. Echocardiography is a useful investigation in the initial work-up of patients with SCLC.