Fourteen patients with pulmonary emboli/infarcts were observed for at least three months by means of computerised tomography. In the acute phase all patients showed minimal changes radiologically, which were not diagnostic of pulmonary emboli; at the same time, computerised tomograms showed definite changes in attenuation in the pulmonary parenchyma and of blood vessels and pleura. A relatively constant and diagnostically valuable sign appears to be a triangular area of attenuation which indicates the presence of an infarct. Serial observations are valuable where there is a clinical suspicion of pulmonary emboli. It is possible to observe regression of the thrombus (due to recanalisation or thrombolysis) and to evaluate the effects of treatment.