The clinical significance of reverse redistribution of technetium-99m sestamibi (MIBI) was investigated in 36 patients with acute myocardial infarction and angiographically confirmed single-vessel disease, but without previous infarction using resting MIBI myocardial single photon emission computed tomography (SPECT) and exercise-reinjection thallium-201 (Tl) myocardial SPECT. MIBI myocardial SPECT was performed 90 min and 300 min after injection of MIBI 370 MBq at rest. Four hours after exercise Tl imaging was completed, reinjection imaging was obtained. Wall motion abnormalities on left ventriculograms were analyzed at the onset of infarction and 1 month later. The severity scores on the MIBI early image, MIBI delayed image and Tl reinjection image were 98 +/- 18, 170 +/- 22 and 90 +/- 18, respectively. The reverse redistribution of MIBI was marked in acute infarction. A significant correlation of severity score was found between the MIBI early image and Tl reinjection image (r = 0.89). In 18 patients with significant stenosis of an infarct-related artery, there was a significant correlation between the degree of reverse redistribution and that of Tl redistribution (r = 0.826). A good correlation was found between the severity score on the MIBI early image and wall motion abnormality at 1 month after infarction (r = 0.816). There was a significant correlation between the degree of reverse redistribution and wall motion improvement (r = 0.782). Despite stenosis of the infarct-related artery, the wall motion abnormality was less in 22 patients with marked reverse redistribution (defect score on the MIBI delayed image was double that on the early image) than the other 14 patients. In conclusion, the MIBI early image may reflect myocardial viability and the reverse redistribution of MIBI was observed frequently in patients with acute myocardial infarction. Marked reverse redistribution was observed in patients with preserved left ventricular function. Because of the close correlation of reverse redistribution with Tl redistribution and wall motion improvement, reverse redistribution of MIBI is considered to occur in areas at risk for acute myocardial infarction.