A newly constructed pressure sensor with a diameter of 0.45 mm was evaluated in 15 patients undergoing balloon coronary angioplasty (PTCA). The sensor and an optic fiber were mounted on a 0.018" guide wire, which was used in the balloon catheter. Pressure gradients were recorded before and after PTCA, respectively. The pressure tracings were of satisfactory quality in all cases. The mean systolic and diastolic gradients before PTCA were 32 +/- 20mm Hg and 44 +/- 26mm Hg, respectively. Pressure gradients were also obtained with the balloon placed in the lesion in order to simulate the conventional way of pressure measurement through the balloon catheter. In this setting, the systolic and diastolic gradients were 77 +/- 32mm Hg and 59 +/- 25mm Hg, respectively. Following balloon dilatation, the systolic pressure gradient decreased to 14 +/- 12mm Hg, and the diastolic gradient to 13 +/- 11mm Hg. In conclusion, this new pressure sensor delivers recordings of good quality and may be especially of interest during angioplasty due to its small diameter.