The perception of abnormal shadows is fundamental to roentgenological diagnosis. A lesion must be greater thancertain limits in size to be roentgenologically visible. On the other hand, considerably larger lesions mayfrequently escape from being detected when they are located in so-called blind areas of the lung fields. Thereseems to be relatively a high intraobserver and interobserver error indetecting and describing abnormal pulmonaryshadows. On this occasion, a brief comment has been made on the variability and limitation in perception ofpulmonary lesions as well as on the advantages and shortcomings of dual interpretation. A few measures which maybe of value in reducing the undesired unreliability of chest X-ray interpretation has also been shortly discussed.