Unlike conventional thallium-201 myocardial imaging, technetium-99m methoxyisobutylisonitrile (MIBI) requires separate stress and rest injections. We prospectively studied 148 consecutive patients referred for myocardial perfusion studies to determine the diagnostic value of rest images once normal exercise or dipyridamole tomographic images had been obtained. In patients referred with no history of previous myocardial infarction in whom the diagnosis of coronary artery disease was suspected, 45 of 109 (41%) patients had normal stress tomographic images. Obtaining rest images did not alter the final interpretation in any of these cases. From this we infer that in patients with normal images after exercise or dipyridamole administration and no past history of myocardial infarction, 99mTc-MIBI rest images are not required. This provides several advantages including increased speed of diagnosis, decreased patient radiation exposure, improved cost efficiency and decreased demand on tomographic camera time.