With a99mTc‐labelled aerosol an inhalation (ventilation) image of the lungs was obtained. A lung perfusion image was obtained with99mTc‐labelled macro‐aggregates. The data from the gamma camera were stored in a computer and the inhalation‐perfusion (I/P) ratio was calculated for the total lung as well as for one half another selected region, and a local (pixel) area. In the anaesthetised dog in sternal recumbency, the I/P ratio decreased from the cranial to the caudal lung regions. Hence in the dog gravity is not the only determinant of the I/P ratio distribution, as it is assumed to be in man. Position and anaesthesia appeared to influence the distribution of I/P ratios within the lung.