A prototype digital chest unit capable of imaging patients in the conventional upright position is described. The unit employs a scanning slit configuration and discrete detec¬tor array. The general features of the detector and data acquisition system are discussed as well as the unit's physical performance parameters and geometry. The resolution along and transverse to the scanning direction is in agreement with theoretical predictions. Measurements of the digital chest unit's signal-to-noise ratio versus detector exposure, detector and data acquisition dynamic range, scatter transmission and exposure linearity are also discussed. © 1981 SPIE.