It has been suggested that a 350 kV technique will produce better chest radiographs than lower kilovoltage techniques. This is because the 350 kV x-ray spectrum provides better penetration of the overlying bony structures and results in a clearer delineation of the mediastinum. Fifty cases, containing 92 definite and significant abnormalities, were selected from a pool of 500 patients who had both 350 and 140 kV chest radiographs on the same day. The 50 paired films were studied at separate times by five experienced radiologists. The interpretations were analyzed for accuracy, significance, and confidence level; interpretation times and the utility of the lateral radiograph were also noted. When all the definitely and potentially significant abnormal findings were considered, the 350 kV films produced fewer true-positive reports and more false-positive reports than the 140 kV films. The receiver operating characteristic (ROC) curves, constructed from the observers' confidence ratings, were shifted toward less satisfactory performance for the 350 kV readings. When only statements about nodules and masses were considered, identical ROC curves were produced by the two techniques. Despite their potential advantages, the 350 kV films showed no diagnostic superiority over the 140 kV films.