In this article we describe a computer program to demonstrate ventilation-perfusion relationships in the lungs, using 99mTc-MAA and 81mKr, with the patients sitting upright, the normal physiological situation. The ventilation and perfusion scans are performed simultaneously with both gamma camera and computer adjusted for dual isotope mode. Steady state images are acquired in the frontal, dorsal, and left and right posterior oblique positions. Additionally, in the dorsal and frontal projections, a sequence of 12 washout images (5 s) is registered, after closing the Krypton supply. After normalization and further computer processing, the following parameters are calculated in the frontal and dorsal projections, in the whole lung and in four horizontal subregions: washout values, ventilation-perfusion ratios, left to right ratios of ventilation and perfusion, and left to right ratios of the average pixel values for ventilation and perfusion. Results in a group of eight healthy volunteers are described and discussed.