Early 99mTc-pyrophosphate (PYP) scintigrams of 29 patients receiving coronary thrombolysis induced by urokinase, 3.9 +/- 1.2 hours after the onset of acute myocardial infarction (AMI), were evaluated. Intravenous 99mTc-PYP scintigraphy was performed 2.8 to 8.0 hours after the onset of AMI. All 19 patients with positive findings on early scintigrams had good recanalization, compared to only 3 of the 10 patients with negative findings. The seven patients with unsuccessful recanalization after coronary thrombolysis had total occlusion or subtotal occlusion with delayed washout of contrast material, and three of them had collaterals. The sensitivity, specificity, and predictive accuracy of positive results of early scintigraphy in predicting the presence of early reperfusion were 73%, 100%, and 90%, respectively. Patients with positive early scintigrams showed increasing regional ejection fraction and decreasing thallium defect scores from the acute stage to the chronic stage. These findings indicate that early 99mTc-PYP scintigraphy is a sensitive noninvasive technique for detecting early recanalization in infarcted vessels. The collateral flow or antegrade flow with delay is not enough to cause 99mTc-PYP uptake in a very early stage of AMI.