Twenty-three consecutive patients with clinical (auscultatory and electrocardiographic) signs of uncomplicated atrial septal defect of secundum or sinus venosus type were examined by chest x-ray, phonocardiography, and echocardiography, before right heart catheterisation. Seventeen (74%) had atrial septal defect, two patients (9%) had insignificant pulmonary stenosis, and four subjects (17%) were normal. No false positive diagnosis of atrial septal defect was made by chest x-ray examination, whereas increased vascular markings were incorrectly interpreted as pulmonary congestion in one case. Four patients had x-ray films showing questionable signs of left-to-right shunt. Six of 15 patients with a large left-to-right shunt were correctly selected for surgery based on radiological findings. One false negative but no false positive diagnosis of atrial septal defect was made by phonocardiography. Four cases with and four cases without atrial septal defect were classified as having questionable phonocardiographic signs of atrial septal defect. Echocardiographic distinction between those with atrial septal defect and those without atrial septal defect was correct in all cases; quantitative measurement of left-to-right shunt, however, was unsatisfactory. Combined normal findings by x-ray film and echocardiography appeared adequate in all cases for the exclusion of atrial septal defect (six patients). When the six patients who were correctly identified for surgery from the radiological findings are included, there was a total of 12 patients out of 23 (52%:95% confidence limits 31 to 73%) who were evaluated definitively by the non-invasive tests.