Myocardial fractional flow reserve (FFR) < 0.75 is a reliable index of a functionally severe coronary stenosis. FFR is best assessed by a sensor-tipped pressure monitoring guidewire (PW). The purpose of this study was to assess whether a multifunctional probing catheter (MFP), a 3 French dual-lumen monorail catheter, can be used to accurately measure intracoronary pressure and FFR. In 35 lesions (35 patients; learning group), we calculated FFR by both PW (FFRPW) and MFP (FFRMFP). Using ROC analysis, the FFRMFP value of 0.65 had the highest sensitivity with the FFRPW < 0.75. FFRMFP cut-off (0.65) was tested in 40 patients (testing group). In all cases, lumen diameter was documented by an intracoronary ultrasound examination. In the learning group, the FFRPW was 0.82 +/- 0.17 and FFRMFP was 0.70 +/- 0.23 (r = 0.88; p < 0.001). The FFRMFP cut-off value (0.65) correctly predicted the FFRPW in 37/40 cases in the testing group. In the 3 discordant cases, FFR was critical (< 0.65) by MFP and normal (> 0.75) by PW. In all these cases, minimal lumen cross-sectional area was < 2.8 mm2. When FFRMFP is > 0.65, FFRPW is always > 0.75. These data demonstrate that even with larger cross-sectional area than a pressure wire, the MFP catheter can easily and reliably be used to assess the functional severity of coronary stenosis.