Single photon emission computed tomography (SPECT) allows separation of radionuclide activity in front of and behind the area of interest and results in more contrast than can be achieved using conventional gamma camera imaging. To determine if this improved contrast is of value in the detection of perfusion abnormalities in the lung, the lower lobe segmental pulmonary arteries of six dogs were embolized and pulmonary perfusion was evaluated using SPECT, conventional gamma camera imaging, and angiography. Although selective segmental angiography was the most sensitive method of detecting emboli, SPECT was much more sensitive than the gamma camera examination in evaluating the effects of the emboli at two hours and one, two, and eight weeks after embolization.