The NLST will generate thousands of serial low dose chest CT scans in a well-defined population, obtained using relatively consistent scanning techniques. These scans are a vital source of data for addressing additional critical issues beyond the primary aim of the NLST, but intimately related to CT screening for lung cancer. The Quality Assurance Working Group and the Publications, Presentations, and Associated Studies (PPA) committee have identified several such research issues which require the NLST CT scans as a primary source of raw data. For example, knowing the observer variability in the interpretation of CT scans is fundamental to evaluating the performance of this screening test. The CT scans obtained during the trial are a ready source of images with which to make this evaluation. As another example of the additional potential value of the NLST CT scans, analysis of the morphologic features of indeterminate lung nodules may help to improve the diagnostic specificity of screening CT examinations. The issue of test specificity is especially relevant to CT screening, due to the relatively high percentage of individuals in the target population with indeterminate pulmonary nodules. The NLST DSMB has recommended that efforts should be made during the trial to pursue this issue. The existing and future NLST CT image data is an especially valuable resource for doing this.