BACKGROUND: The achievement of maximal vasodilatation is mandatory for coronary flow reserve (CFR) and fractional flow reserve (FFR) measurements. Recent studies indicated that incremental dose or high dose of adenosine was necessary to achieve maximal hyperemia, but the optimal bolus dose of adenosine in Koreans is not well-known. This prospective study was designed to examine the dose-response and optimal dose of adenosine in CFR and FFR measurements in Koreans. METHIDS: CFR: CFR was measured in 40 consecutive patients with angiographically normal coronary arteries using a FloWire (Endosonics). Three different doses (9,18 and 36關g) of adenosine were used. FFR: 102 consecutive patients with 188 intermediate lesions (160 left coronary (LCA) and 28 right coronary (RCA) lesions) underwent determination of FFR. FFR was measured with a RADI 4 pressure wire (RADI Medical Systems). Three different bolus doses of adenosine (18, 36 and 72關g) were administered in an incremental fashion. RESULTS: CFR: 18關g adenosine had tendency to achieve higher CFR than 9 關g (2.7짹0.64 vs. 2.8짹0.72, p= 0.08). But when we increased adenosine upto 36關g, CFR fell off significantly comprared to using 18 關g adenosine (2.8짹0.72 vs. 2.6짹0.72, p<0.01). FFR: The dose of adenosine which achieved maximal hyperemia was 51짹16 關g in LCA and 35짹20 關g in RCA. In 73 (46%) of LCA and 12(42%) of RCA lesions, further reduction of FFR occurred when a high dose of adenosine was injected (LCA>36ug, RCA> 18關g). But further reduction of FFR did not influence on the clinical decision. Ten episodes of AV block (LCA (3) vs. RCA(7)) occurred with high dose of adenosine and it significantly delayed procedure time. CONCLUSION: This study suggests that more than 18 關g adenosine does not have additive effect on CFR measurment and that doses of adenosine up to 36關g in left and 18關g in right coronary lesions are optimal for intracoronary bolus injection to measure FFR. Higher dose did not influence on the clinical decision and delayed procedure time due to bradycardia.