Chest radiographs obtained with mobile equipment for 240 kVp phototimed technique and conventional technique were compared in 161 patients. Features of interest were visualization of air space, interstitium, mediastinum, pleura and vessels, tracheobronchial tree, catheters and tubes. The 240 kVp system demonstrated consistently good visualization of central air passages, hilar contours, and pulmonary detail. It was superior to the conventional portable in eliminating respiratory motion, defining lung infiltrates, and localizing the endotracheal tube relation to the carina. The 240 kVp system had noticeable deficiencies in depicting calcifications, bone detail, and fat planes. These deficiencies were not of clinical significance. Although the equipment was compact, easily maneuverable, and simple to operate, the cassette holder was somewhat heavy--a detrimental but manageable factor. Another shortcoming was poor visualization of homogeneously opacified catheters within the mediastinum, although catheters with a dense radiopaque stripe alleviated this problem.