Selected difficult chest radiographs were interpreted by 10 radiologists and then reread in a Focused Search condition that directed readers'' attention to film regions containing frequently omitted findings. The percentage of true abnormalities reported at any level of confidence increased from 49.3-68.3 between the usual and Focused Search conditions. However, the corresponding percentage of significant false positives also increased from 4.6-10.6. The separate ROC [receiver operating characteristic] curves from each condition could be superimposed and the data fit by a single ROC curve. Thus, the reduced omissions in Focused Search were the result of less stringent criteria for reporting the presence of abnormal findings, rather than an enhanced ability to detect abnormalities. There was no evidence that the original omissions were abnormalities simply overlooked in faulty initial searches.