This is a report on the testing of a novel system of radiography of the thorax consisting of a combination of moving-slit radiography with a slot-type image intensifier (proximity focussed linear image intensifier), being thus a variant of rotational scanography (or a swinging slot x-ray machine), the image scale being 1:1. The system was compared with conventional x-ray film/foil technique using a group of 115 patients. Special features of the new system are a very low irradiation exposure dose and a 100 x 100 mm size image. It is shown that the imaging method is highly efficient in respect of the examined nine classes of findings and that the image quality of large-size thorax x-ray films is very nearly attained. The low exposure dose, low running cost and advantages in storing and indexing can serve as counter-arguments against the well-known reserved attitude in respect of a medium-size format. The system opens good future possibilities especially with regard to follow-up and monitoring of selected patient groups (e.g. blood donors, medical personnel).