We designed a new method to evaluate the rate of change of myocardial 99mTc-tetrofosmin (TF) uptake between exercise and rest images with a 1-day protocol. Fifteen normal cases were studied. A 370 MBq of TF was injected at peak exercise. Initial (TF1) and delayed (TF2) exercise SPECT images were acquired 30 min and 3 hr after the injection. A 740 MBq of TF was reinjected soon after TF2 acquisition, and rest SPECT images (TF3) were obtained 30 min after the reinjection. Myocardial counts of TF1, TF2 and TF3 were defined C1, C2 and C3 respectively. Then, the rate of change of myocardial TF uptake between exercise and rest (delta MTU: delta myocardial TF uptake) was determined by the following formula. delta MTU = [(C1/(C3-C2)] x R-1] x 100 (%) (R: dose ratio). delta MTU was 57.8 +/- 9.9% in normal cases and roughly correlated with maximal heart rates and double product. If the extraction fraction of TF is not changed under the exercise and resting condition, delta MTU may have some relation with the coronary flow/cardiac output ratio at exercise. In conclusion, delta MTU is a useful index to evaluate coronary flow reserve non-invasively.